the following description of the embodiments of the present invention makes reference to the drawings . fig1 is an example of a color sorter , showing an exterior perspective view thereof . fig2 shows a simplified side sectional view of the color sorter shown in fig1 . the color sorter 1 in question is provided with a loading hopper 2 for loading particulate matter ; a bucket conveyor 3 for lifting the particulate matter up into the top part of the sorter 1 ; a storage tank 4 for storing the lifted particulate matter ; a rotary valve 5 arranged in the outlet of the storage tank 4 ; a sloping chute 6 having predetermined width , arranged below the rotary valve 5 ; a pair of optical detection devices 7 a , 7 b arranged to the front and back with the sloping chute 6 therebetween ; an ejector system 8 arranged below the optical detection devices 7 a , 7 b ; and a particulate matter discharge trough 9 arranged below the ejector system 8 . the optical detection devices 7 a , 7 b are provided with sensors 10 a , 10 b , mirrors 11 a , 11 b , illumination means 12 a , 12 b , and background means 13 a , 13 b . as the sensors 10 a , 10 b , there are employed ccd line sensors or the like , constituted by a plurality of photodetector elements concatenated in a line pattern and assigned to a position in the width direction of the sloping chute 6 , for example . the background means 13 a , 13 b are arranged to the back of a particulate matter detection position o on the optical axes of the sensors 10 a , 10 b . the optical detection devices 7 a , 7 b are adapted to detect particulate matter falling from the bottom edge of the sloping chute 6 , at positions in the width direction of the falling trajectory thereof . the ejector system 8 is also provided with a nozzle part 20 having a plurality of nozzle holes assigned to positions in the width direction of the sloping chute 6 . based on the results detected by the optical detection devices 7 a , 7 b , particulate matter falling from the bottom edge of the sloping chute 6 is carried away by jets of air from nozzle holes at corresponding positions in the width direction of the falling trajectory thereof . the particulate matter discharge trough 9 is provided with a satisfactory item discharge trough 9 a arranged along the falling trajectory of the particulate matter from the bottom edge of the sloping chute 6 , and with an unsatisfactory item discharge trough 9 b arranged at a position allowing the falling trajectory of the particulate matter to be modified by a jet of air from a nozzle hole of the nozzle part 20 constituting the ejector system 8 . in the color sorter 1 , particulate matter loaded into the loading hopper 2 is lifted by the bucket conveyor 3 and stored in the storage tank 4 . the particulate matter , which is supplied from the storage tank 4 at a constant flow rate via the rotary valve 5 , spreads out across the width direction of the sloping chute 6 , and flows down naturally in a continuous manner . falling particulate matter having been launched into the air from the bottom edge of the sloping chute 6 is illuminated by the illumination means 12 a , 12 b of the pair of optical detection devices 7 a , 7 b , and with the background means 13 a , 13 b as the background , is imaged by the sensors 10 a , 10 b at a particulate matter detection position o extending linearly in the width direction of the sloping chute 6 , whereby unsatisfactory items or foreign matter are identified by comparing the voltage value of the image signal to a reference threshold value , or the like . particulate matter identified as being satisfactory items then falls into the satisfactory item trough 9 a arranged along a predetermined falling trajectory . particulate matter identified as being unsatisfactory items or foreign matter is carried away by air jetted at predetermined timing from a nozzle hole that opens onto a predetermined position of the nozzle part 20 constituting the ejector system 8 , and falls into the unsatisfactory item trough 9 b . alternatively , satisfactory items , instead of unsatisfactory items or foreign matter , may be the particulate matter that is carried away by air in this way . fig3 is a perspective view of an ejector system in an embodiment of the present invention . fig4 is a fragmentary enlarged front view of the ejector system shown in fig3 . as shown in fig3 , the ejector system 8 in the present embodiment is constituted by a nozzle part 20 and a manifold part 30 . the nozzle part 20 is constituted by screwing together a nozzle upper member 20 a and a nozzle lower member 20 b . the manifold part 30 is constituted by screwing together a manifold upper member 30 a and a manifold lower member 30 b . here , as will be clear from fig4 , a plurality of nozzle holes 21 open along the width direction at the front surface of the nozzle part 20 . moreover , as shown in fig3 and 4 , at one side end of the upper surface of the nozzle part 20 , there is arranged an air sweeper 23 provided with nozzles 22 that open towards the other side end of the upper surface thereof . an attachment member 31 for attaching the ejector system 8 to the color sorter is screwed to the front of the upper face of the manifold upper member 30 a . fig5 shows a view of the ejector system shown in fig3 , with the nozzle part and the manifold part exploded . fig6 is a perspective view of the exploded manifold part . as shown in fig5 , a laterally elongated recess part 32 is formed on the front surface of the manifold part 30 , and a pair of rods 33 a , 33 b are formed at either side of the recess part 32 . meanwhile , a laterally - elongated projection part 24 is formed on the back surface of the nozzle part 20 , and a pair of through - holes 25 a , 25 b are formed at either side of the projection part 24 . here , as will be clear from fig6 , a plurality of air flow paths 37 communicating with the nozzle holes 21 open along the width direction into the recess part 32 formed on the front surface of the manifold part 30 . attachment holes 34 a , 34 b for the pair of rods 33 a , 33 b are formed at either side of the recess part 32 . as shown in fig4 and 6 , a plurality of electromagnetic valves 35 a , 35 b are arranged , in correspondence with the air flow paths 37 that open into the recess part 32 , along the width direction on the back face of the manifold upper member 30 a and of the manifold lower member 30 b . a pair of air line connection parts 36 a , 36 b for connecting compressed air supply lines are arranged on the lower surface of the manifold lower member 30 b . here , as will be clear from fig4 , the electromagnetic valves 35 a , 35 b are arranged in a phase - shifted state in the width direction , with respect to the manifold upper and lower members 30 a , 30 b . as the electromagnetic valves 35 a , 35 b there may be employed any of the widely known types , and therefore a description is omitted here . in the ejector system 8 of the present embodiment , the nozzle part 20 and the manifold part 30 are integrated by inserting the pair of rods 33 a , 33 b attached to the manifold part 30 into the pair of through - holes 25 a , 25 b formed in the nozzle part 20 ; and in a state in which the projection part 24 formed on the back surface of the nozzle part 20 has been mated into the recess part 32 formed on the front surface of the manifold part 30 , female thread parts of fastening members 26 a , 26 b shown in fig5 are threaded and tightened onto distal end male thread parts of the rods 33 a , 33 b that project out through the through - holes 25 a , 25 b . in the ejector system of the present embodiment , because the nozzle part 20 and the manifold part 30 are integrated through tightening of the fastening members 26 a , 26 b , the nozzle part 20 and the manifold part 30 can be easily separated , for improved cleaning and maintenance performance . next , fig7 shows a plan view , in the detached state , of the nozzle upper member and the manifold upper member of the ejector system shown in fig3 . fig8 shows a bottom view of the nozzle upper member and the manifold upper member in the detached state in fig7 . as shown in fig7 , a plurality of slots 37 b , 27 b continuing in the width direction from the front of the manifold lower member 30 b to the front end of the nozzle lower member 20 b are formed on the upper surfaces of the nozzle and manifold lower members 20 b , 30 b . at the back of the upper face of the manifold lower member 30 b , there is formed an air space recess part 40 b that opens onto the lower surface through air supply holes 39 a , 39 b . a plurality of communicating holes 38 b are formed across the width direction of the manifold lower member 30 b . the air space recess part 40 b communicates with the plurality of electromagnetic valves 35 b that have been arranged on the back surface of the manifold lower member 30 b . the communicating holes 38 b communicate at the back end with the electromagnetic valves 35 b , and communicate alternately at the front end with the slots 37 b formed at the front of the manifold lower member 30 b . as shown in fig8 , a plurality of slots 37 a , 27 a continuing in the width direction from the front of the manifold upper member 30 a to the front end of the nozzle upper member 20 a are formed on the lower surfaces of the nozzle and manifold upper members 20 a , 30 a . at the back of the lower face of the manifold upper member 30 a , there is formed an air space recess part 40 a . a plurality of communicating holes 38 a are formed across the width direction of the manifold upper member 30 a . the air space recess part 40 a communicates with the plurality of electromagnetic valves 35 a that have been arranged on the back surface of the manifold upper member 30 a . the communicating holes 38 a communicate at the back end with the electromagnetic valves 35 a , and communicate alternately at the front end with the slots 37 a formed at the front of the manifold upper member 30 a . in the ejector system of the present embodiment , a plurality of independent air passages 27 , 37 affording communication between the nozzle holes 21 and the communicating holes 38 a , 38 b are constituted by the slots 27 b , 37 b formed on the upper surfaces of the nozzle and manifold lower members 20 b , 30 b shown in fig7 , and the slots 27 a , 37 a formed on the lower surfaces of the nozzle and manifold upper members 20 a , 30 a shown in fig8 . at this time , the slots 37 b that communicate with the communicating holes 38 b formed in the manifold lower member 30 b constitute air passages to the slots 37 a that do not communicate with the communicating holes 38 a formed in the manifold upper member 30 a . the slots 37 b that do not communicate with the communicating holes 38 b formed in the manifold lower member 30 b constitute air passages to the slots 37 a that communicate with the communicating holes 38 a formed in the manifold upper member 30 a . a communicating hole 29 communicating with the upper surface of the nozzle upper member 20 a is formed in the slot 28 a that has been formed at the left end of the lower surface of the nozzle upper member 20 a shown in fig8 . the slot 28 a in question constitutes an air passage 28 communicating with the slot 28 b that has been formed at the left end of the upper surface of the nozzle lower member 20 b shown in fig7 , as well as with the nozzles 22 of the air sweeper 23 arranged on the upper surface of the nozzle part 20 in the ejector system of the present embodiment , an air space 40 , discussed below , is constituted by the air space recess part 40 b formed in the upper surface of the manifold lower member 30 b shown in fig7 , and the air space recess part 40 a formed in the lower surface of the manifold upper member 30 a shown in fig8 . the air space 40 is a space for storing compressed air supplied from a compressed air source , not shown , to the air supply holes 39 a , 39 b that open onto the lower surface of the manifold lower member 30 b . fig9 shows an air flow path inside the nozzle part and the manifold part , taken along section a - a in fig3 . fig1 shows an air flow path inside the nozzle part and the manifold part , taken along section b - b in fig3 . the air flow path shown in fig9 , via the electromagnetic valve 35 b arranged in the manifold lower member 30 b , affords communication between the air space 40 formed in the manifold part 30 and the communicating hole 38 b formed in the lower member 30 b ; and via the air flow path 37 formed at the front of the manifold part 30 and the air flow path 27 formed in the nozzle part 20 , affords communication with the nozzle hole 21 that opens onto the front surface of the nozzle part 20 . the air flow path shown in fig1 , via the electromagnetic valve 35 a arranged in the manifold upper member 30 a , affords communication between the air space 40 formed in the manifold part 30 and the communicating hole 38 a formed in the upper member 30 a ; and via the air flow path 37 formed at the front of the manifold part 30 and the air flow path 27 formed in the nozzle part 20 , affords communication with the nozzle hole 21 that opens onto the front surface of the nozzle part 20 . the air flow paths shown in fig9 and 10 supply air from the air space 40 to the nozzle holes 21 through opening of the electromagnetic valves 35 a , 35 b . for example , in the color sorter 1 shown in fig1 and 2 , in a case in which an unsatisfactory item is detected by the optical detection devices 7 a , 7 b , and a position in the width direction of the falling trajectory of the particulate matter detected to be an unsatisfactory item corresponds to the position of the nozzle holes 21 shown in fig9 or 10 , the ejector system 8 of the present embodiment will open the electromagnetic valve 35 a , 35 b shown in fig9 or 10 , and thereby jet high pressure air stored in the air space 40 , from either of the aforedescribed nozzle holes 21 over the predetermined air flow path . fig1 shows an air flow path inside the nozzle part and the manifold part , taken along c - c in fig3 . the air flow path shown in fig1 , via the electromagnetic valve 35 a arranged in the manifold upper member 30 a , affords communication between the air space 40 formed in the manifold part 30 and the communicating hole 38 a formed in the upper member 30 a ; and via the communicating hole 29 , affords communication between the air flow path 37 formed at the front of the manifold part 30 and the air flow path 28 formed in the nozzle part 20 , and the nozzle 22 of the air sweeper 23 arranged on the upper surface of the nozzle part 20 . the air flow path shown in fig1 likewise supplies the nozzle 22 of the air sweeper 23 with air from the air space 40 , through opening of the electromagnetic valve 35 a . for example , by utilizing a timer in the color sorter 1 shown in fig1 and 2 to periodically open the electromagnetic valve 35 a and jet air from the nozzle 22 depending on the running time of the color sorter 1 , or by utilizing a sensor to open the electromagnetic valve 35 a and jet air from the nozzle 22 depending on the condition of accumulation of dust or the like on the upper surface of the nozzle part 20 , the upper surface of the nozzle part 20 can be cleaned automatically . moreover , by switching the opening / closing action of the electromagnetic valve 35 a to manual , the upper surface of the nozzle part 20 can be cleaned automatically through manual operation by a worker . in the above manner , in the ejector system 8 of the present embodiment , the nozzle part 20 and the manifold part 30 are constituted such that it is possible for them to be easily assembled and separated , improving the cleaning and maintenance performance . moreover , in the ejector system 8 of the present embodiment , the nozzle part 20 and the manifold part 30 are constituted by screwing together upper and lower members , and therefore the upper and lower members can be easily separated , so that the air passages 27 , 37 formed on the opposed surfaces of the upper and lower members can be easily cleaned . in the ejector system 8 of the present embodiment , at one side end of the upper surface of the nozzle part 20 , there has been arranged the air sweeper 23 provided with nozzles 22 that open towards the other side end of the upper surface of the nozzle part 20 , whereby starting material , dust , and the like accumulating on the upper surface of the nozzle part 20 can be cleaned automatically , and the burden of cleaning or maintenance performed by workers can be reduced . the ejector system 8 of the present embodiment is constituted such that when the plurality of electromagnetic valves 35 a , 35 b are respectively arranged on the upper and lower members 30 a , 30 b constituting the manifold part 30 , the phase of the electromagnetic valves 35 a arranged on the upper member 30 a and that of the electromagnetic valves 35 b arranged on the lower member 30 b are made different from one another , and therefore the number of nozzle holes that open onto the front surface of the nozzle part can be increased to double , as compared with a case in which the electromagnetic valves are arranged on one member only . in the ejector system of the aforedescribed embodiment , the nozzle part 20 and the manifold part 30 are integrated by inserting the pair of rods 33 a , 33 b attached to the manifold part 30 into the pair of through - holes 25 a , 25 b formed in the nozzle part 20 , and threading and tightening the female thread parts of the fastening members 26 a , 26 b onto the distal end male thread parts of the rods 33 a , 33 b that project out through the through - holes 25 a , 25 b ; however , the nozzle part 20 and the manifold part 30 may be integrated by other means . in the ejector system of the aforedescribed embodiment , the air flow paths 27 , 37 that are formed on the opposed surfaces of the upper and lower members of the nozzle part 20 and the manifold part 30 are constituted by slots formed in the upper surface of the lower members and slots formed in the lower surface of the upper members ; however , provided that the air flow paths 27 , 37 are formed in the opposed surfaces of the upper and lower members of the nozzle part 20 and the manifold part 30 , it is acceptable for the slots constituting the air flow paths 27 , 37 to be formed in either the upper or lower member only . in the ejector system of the aforedescribed embodiment , the nozzle part 20 and the manifold part 30 are respectively constituted by screwing together an upper and a lower member ; however , these could be respectively constituted as single members . in this case , the air flow paths formed in the parts may be formed as through - holes . in the ejector system of the aforedescribed embodiment , the air sweeper 23 is arranged on the upper surface of the nozzle part 20 ; however , the arrangement of the air sweeper 23 is arbitrary . in the ejector system of the aforedescribed embodiment , the electromagnetic valves 35 are arranged in two rows on the manifold part 30 ; however , the electromagnetic valves 35 may instead be arranged in three or more rows , or arranged in a single row only , as in the prior art . fig1 is an example of implementation of the ejector system of the present invention in a color sorter , and shows a partial enlarged view of fig2 . as shown in fig1 , the ejector system 8 of the present embodiment is fastened to the body of the color sorter by the attachment member 31 , which has been screwed to the upper surface at the front of the manifold upper member 30 a . in the process , the ejector system 8 is arranged such that the nozzle part 20 is positioned on the flow path of the particulate matter , and the manifold part 30 is positioned in the interior of the sorter body . in the ejector system 8 of the present embodiment , because the manifold part 30 is positioned in the interior of the sorter body , soiling of the electromagnetic valves by dust and the like stirred up within the flow path in association with falling of the particulate matter can be prevented . the ejector system 8 of the present embodiment is not limited to application in the aforedescribed color sorter 1 ; implementation in all manner of color sorters is possible . the present invention is not limited to the aforedescribed embodiments ; various modifications of the constitution thereof can be made , as appropriate , without departing from the scope of the claims . the ejector system employed in the color sorter of the present invention has excellent cleaning and maintenance performance by virtue of a constitution whereby the nozzle part and the manifold part are integrated by a separable structure , and the application value is accordingly high .