hereinafter , an embodiment of the present invention will be described with reference to the drawings . fig1 is a perspective view of an engine generator which is an engine powered working machine according to an embodiment of the present invention . the engine generator 1 includes wheels wf so as to be movable . in the present specification , the side on which the wheels wf are provided is referred to as a “ front ” of the engine generator 1 , and the direction in which the wheels wf have axles extended is referred to as a “ width direction .” the engine generator 1 includes a generator frame 7 formed of a main frame 2 made of a pipe , a pair of upper sub - frames 3 , 3 extending to the front and rear in an upper portion of the main frame 2 , a front sub - frame 4 extending in the width direction in a lower portion of the main frame 2 , a pair of bottom sub - frames 5 , 5 extending in the width direction in the lower portion of the main frame 2 , and a tank support frame 6 both ends of which are connected to four corners of the main frame 2 at locations closer to the upside of the main frame 2 , respectively . one of the bottom sub - frames 5 , 5 that is closer to the front supports an axle 8 of the wheel wf , and the other of the bottom sub - frames 5 , 5 that is closer to the rear supports a pair of stands 9 ( only one of them is shown ) disposed separated in the width direction . the bottom sub - frames 5 , 5 further carry an engine 10 and a generator 11 placed thereon . an air cleaner 13 is disposed in the rear of a cylinder head 12 of the engine 10 , and a muffler 14 is disposed at one side of the generator 11 ( left side when viewed from the rear of the engine generator 1 ). at the other side ( right side when viewed from the rear of the engine generator 1 ) of the generator 11 , an operation panel 15 ( a back side of which is shown ) including a control unit and a display unit is disposed . the tank support frame 6 is provided with brackets ( not shown ) at four corners , and by fixing four sites of a top - bottom mating portion that overhangs circumferentially from the middle in an upper and lower direction of a fuel tank 16 to the brackets by use of bolt - and - nut 17 sets , the fuel tank 16 is carried on the generator frame 7 . the pair of upper sub - frames 3 , 3 have handles 19 , 19 that are attached by use of clamps 18 , 18 , respectively . end portions of the handles 19 , 19 are covered with rubber grips 20 , 20 that can be gripped by an operator . the engine generator 1 having this configuration includes a known recoil starter ( not shown ) of the engine 10 that is adjacent to the right side of the air cleaner 13 , and the engine 10 is rotated by pulling a rope of the recoil starter . the generator 11 rotates to generate power when the engine 10 is rotated by the recoil starter , a fuel pump ( described later in detail ) is driven by the control unit that is being started by the generated power , and fuel is supplied under pressure from the fuel tank 16 to a fuel injection valve ( not shown ) of the engine 10 responsive to an ignition signal of the engine 10 being output . the engine 10 is started when the fuel is fed together with air to a combustion chamber according to the fuel injection valve opening at a predetermined timing and the mixture is ignited by an ignition device ( not shown ). when the engine 10 starts , the generator 11 starts power generation , conventionally known control is performed to continue the power generating operation , and an output voltage of the generator 11 is connected to a predetermined output end ( outlet or socket ). the outlet may be provided on an operation panel 15 . next , a fuel pump to be mounted on the fuel tank 16 will be described . fig2 is a front view of the engine generator 1 . in fig2 , the engine 10 is formed of a crankcase 21 and a cylinder head 12 that sticks out obliquely upward from the crankcase 21 toward a bottom surface of the fuel tank 16 . the fuel tank 16 is located above the engine 10 and generator 11 . because the bottom surface of the fuel tank 16 is flat , it looks as if there were no large space between the engine 10 and generator 11 and the fuel tank 16 , but a relatively large space exists between the fuel tank 16 having a flat bottom surface and the engine 10 and generator 11 whose external form or outline is irregular . particularly , the cylinder head 12 sticks out obliquely upward and thus has a small gap with the fuel tank 16 , but the outer peripheral shape of the crankcase 21 is an arc , the crankcase 21 is located lower than the cylinder head 12 , and there is thus a relatively large space produced between the crankcase 21 and the fuel tank 16 . therefore , a fuel pump 22 is disposed in the space produced between the crankcase 21 and the fuel tank 16 . to the bottom surface of the fuel tank 16 , an extended portion ( expansion box ) 23 of the fuel tank 16 is joined , and the fuel pump 22 whose external form is generally cylindrical is mounted from below on the extended box 23 . the fuel pump 22 has a fuel intake port 24 facing the interior of the expansion box 23 , and a filter 25 attached to the fuel intake port 24 is housed inside the expansion box 23 . since the fuel intake port 24 and the filter 25 are located inside the expansion box 23 extended downward from the fuel tank 16 , the capacity of the fuel tank 16 can be effectively used . the fuel pump 22 is connected at a discharge port with a fuel pipe 26 , and an end portion of the fuel pipe 26 is connected to a fuel injection valve ( injector ) 27 provided in the engine 10 . fig3 is a view showing a modification ( second embodiment ) of a mounting mode of a fuel pump , and the same reference signs as those in fig2 denote the same or equivalent parts . in the example of fig3 , the expansion box 23 is extended further downward to expand the capacity of the expansion box 23 . the capacity of the fuel tank 16 is substantially expanded by using the space produced between the crankcase 21 and the fuel tank 16 as large as possible . unlike the case of supplying fuel by a carburetor system , since the fuel pump 22 can be at any height position in the engine 10 including a fuel injection system , the expansion box 23 can be extended downward so far as the space permits to secure a larger fuel retention capacity . fig4 is a sectional view of a fuel pump according to a third embodiment of the present invention . fig5 is a perspective view showing an interior of a pump case , fig6 is a perspective view of a case body of the pump case viewed from above , fig7 is a perspective view of the case body 31 viewed from below , and the same reference signs as those in fig4 denote the same or equivalent parts . in fig4 to fig7 , the fuel pump 22 is housed in a pump case 30 and mounted on the fuel tank 16 . the pump case 30 consists of a case body 31 and a cap 32 that covers a bottom portion of the case body 31 , and a flange 33 for mounting is provided at an upper portion of the case body 31 . on the other hand , a mounting seat ( annular plate ) 34 that receives the flange 33 of the case body 31 is joined by a method such as welding to the bottom surface of the fuel tank 16 . the mounting seat 34 includes female screws 35 at a plurality of sites ( for example , four sites ), and bolts 36 inserted through bolt through - holes 29 provided in the flange 33 of the case body 31 so as to be aligned with the female screws 35 are screwed in the female screws 35 , respectively . the flange 33 includes a seal groove formed on a surface opposed to the mounting seat 34 , and seal between the flange 33 and the mounting seat 34 is secured by an o - ring 37 that fits in the seal groove . the case body 31 is a cylinder body , and further includes in its interior an inner cylinder body 38 that holds the fuel pump 22 . the inner cylinder body 38 is provided eccentrically with respect to an axis of the cylindrical case body 31 , and has an inner diameter “ d ” that is adapted to the external size of the fuel pump 22 . the inner cylinder body 38 is open at the top and bottom , and the fuel intake port 24 passes through the open part of the upper portion and the filter 25 is attached to the end of the fuel intake port 24 , that is , the side of the fuel tank 16 . the surroundings of the inner cylinder body 38 are open at an upper portion to communicate with the fuel tank 16 , and a lower portion thereof excluding a regulator housing portion 39 is closed . the regulator housing portion 39 is a cylinder body extending parallel to the inner cylinder body 38 , and houses a pressure regulator 40 . the pressure regulator 40 can have a well - known structure formed of a valve and a spring . the regulator housing portion 39 is covered with a pressure stabilizing tube 41 . the pressure stabilizing tube 41 is extended to the inside of the fuel tank 16 , and performs a function of returning the back pressure of the pressure regulator 40 to a gaseous phase . returning the back pressure of the pressure regulator 40 to a gaseous phase allows stabilization of the discharge pressure of the fuel pump 22 . it is preferable to provide the pressure stabilizing tube 41 in the sense of better stabilization of the discharge pressure , but the pressure stabilizing tube 41 is not essential . the cap 32 includes a connector portion 42 to which the fuel pipe 26 is joined . the cap 32 also includes an electrode 45 for connecting a lead wire 43 that supplies a drive motor ( not shown ) of the fuel pump 22 with electricity to an external harness 44 . it is preferable to mold the electrode 45 integrally with the cap 32 . in the third embodiment , an example of the pump case 30 mounted on the bottom surface 16 has been shown , but this structure may be applied to the first and second embodiments so as to mount the pump case 30 housing the fuel pump 22 on a bottom surface of the expansion box 23 . during operation of the fuel pump 22 , the fuel inside the fuel tank 16 passes through the filter 25 located at a lowermost portion of the fuel tank 16 , and is introduced into the fuel pump 22 from the fuel intake port 24 . then , the fuel discharged from the discharge port 46 is retained in a space ( buffer ) 47 between the case body 31 and the cap 32 . the pressure of the fuel retained in the buffer 47 is regulated to a constant pressure by the pressure regulator 40 . further , the fuel is discharged from the connector portion 42 of the cap 32 , and fed to the injector 27 through the fuel pipe 26 described above . although the present invention has been described in accordance with the embodiments , the present invention is not limited to these embodiments , and modifications can be made based on the matters described in the claims and the known art . for example , it suffices that the fuel pump 22 is disposed in a manner projecting in the space between the fuel tank 16 and the engine 10 and generator 11 , without limitation to providing at a position close to a bottom portion of the crankcase 21 . moreover , the engine working machine is not limited to a generator that is driven by an engine , and may be a water pump that is driven by an engine .