referring now to the drawings , there is shown in fig2 an electron source k according to one embodiment of the present invention . the electron source k includes a metallic substrate 1 , a plurality of linear thermionic cathodes 3 for emitting electron beams , a striped cathode support means 2 for supporting the cathodes 3 and a grid electrode 4 . the cathodes 3 are provided so as to intersect with the cathode support means 2 . the cathode support means 2 is provided on the substrate 1 , while the grid electrode 4 is provided above and substantially in parallel with the cathodes 3 . the cathode support means 2 is provided between the substrate 1 and the cathodes 3 so as to prevent vibrations of the cathodes 3 . the cathode support means 2 includes a striped metallic element 2a and a heat resistant insulating member 2b . by deposition , frame spraying , etc ., the insulating member 2b having a width several times a thickness of the cathodes 3 is formed on the substrate 2a , at such portions of the striped metallic element 2a as to be brought into contact with the cathodes 3 . furthermore , a signal electrode 5 for controlling the electron beam emitted by the cathode 3 is provided in the vicinity of the cathode 3 as shown in fig3 showing only periphery of the cathode 3 and the cathode support means 2 . in fig3 the cathode 3 is strained so as to be lightly pressed against the insulating member 2b . the signal electrode 5 is formed on the striped metallic element 2a so as to interpose the insulating member 2b therebetween . in this embodiment , the signal electrode 5 is electrically connected to the metallic element 2a . although not specifically shown , all the above mentioned components of the electron source k are enclosed in a vacuum vessel . in fig2 b ; the striped cathode support means 2 is formed on the substrate 1 and a plurality of the linear thermionic cathodes 3 are provided so as to intersect with the cathode support means 2 . the latticed electron beam lead - out electrode 4 is provided above the linear thermionic cathodes 3 . by applying a voltage to the control electrode 5 , the electron beam 6 is emitted from the cathode 3 . in order to control the electron beam 6 for each of the cathodes 3 , various methods can be employed in which , for example , a voltage applied to each cathode 3 itself is controlled and the electron beam is selected after having been emitted from the electron source . if the former method is employed , the electron beam can be obtained from only aperture 4a as shown in fig2 b . the operation of the electron source k of the above described arrangement is described hereinbelow . in fig2 a , when a voltage which is positive relative to the cathode 3 is applied to the grid electrode 4 so as to heat the cathode 3 to temperatures enabling emission of electrons therefrom and a predetermined potential is imparted to the signal electrode 5 , the areas in the vicinity of the cathode 3 corresponding to a portion of the signal electrode 5 having the predetermined potential imparted thereto partially has an electric field in which electrons can be emitted from the cathode 3 . as a result , an electron beam 6 is emitted from the cathode 3 . when a portion 3a of the cathode 3 is held in contact with the cathode support means 2 so as to correspond to one aperture 4a of the grid electrode 4 and is interposed by two neighboring portions 3b and 3c of the cathode 3 held in contact with the cathode support means 2 , electron beams are taken out mainly from vicinity of the portion 3a of the cathode 3 through the one aperture 4a of the grid electrode 4 . therefore , since a distance between the one aperture 4a of the grid electrode 4 confronting the portion 3a of the cathode 3 and each of the two neighboring portions 3b and 3c of the cathode 3 not confronting the one aperture 4a is increased approximately to a control pitch of the electron beams as compared with that of prior art electron sources , the electron beams emitted from an electron beam emitting portion of the cathode 3 , namely , from vicinity of the portion 3a of the cathode 3 held in contact with the cathode support means 2 pass through only the corresponding one aperture 4a of the grid electrode 4 . at this time , the area in the vicinity of a portion of the insulating member 2b held in contact with the cathode 3 is electrically charged to a potential approximately identical with that of the cathode 3 . thus , without influence exerted by the signal electrode 5 , a state is brought about in which electron beams are emitted at all times . however , in this embodiment , since the signal electrode 5 for controlling electron beams is formed integrally with the cathode support means 2 in contrast with prior art electron sources , a distance between the cathode 3 and the signal electrode 5 is reduced greatly in comparison with prior art electron sources . therefore , a switching voltage required for turning on and off electron beams can be significantly lowered . fig4 shows an electron source k &# 39 ; which is a modification of the electron source k . the modified electron source k &# 39 ; includes a cathode support means 2 &# 39 ;. the cathode support means 2 &# 39 ; includes a metallic element 2c acting also as the signal electrode 5 of the electron source k and a heat resistant insulating member 2b provided on the metallic element 2c . at a portion of the substrate 2c , which is brought into contact with the cathode 3 , the insulating member 2b is so formed as to have a width smaller than that of the electron source k . therefore , even if the signal electrode 5 is not provided separately , emission of electron beams from the cathode 3 can be controlled sufficiently by a potential applied to the metallic element 2c . by this arrangement of the electron source k &# 39 ;, the electron source k &# 39 ; is structurally simplified and its production cost can be lowered . as is clear from the foregoing , the structure of the electron source of the present invention is made relatively simple . furthermore , in accordance with the present invention , not only generation of leaked electron beams is substantially eliminated without increasing the control pitch of electron beams but emission of electron beams can be controlled at a relatively low switching voltage . although the present invention has been fully described by way of example with reference to the accompanying drawings , it is to be noted here that various changes and modifications will be apparent to those skilled in the art . therefore , unless otherwise such changes and modifications depart from the scope of the present invention , they should be construed as being included therein .