as shown in fig3 which illustrates the construction of the injection interval adjusting device 8 two rotary shafts 9 10 are axially supported rotatably and parallel to each other inside a frame 15 the rotary shaft 9 is provided with a cam 11 and a helical gear 16 of a greater length the rotary shaft 10 is axially supported slidably in the axial direction relative to the frame 15 and is provided with a cam 12 and a helical gear 17 which is meshed with the helical gear 16 this cam 12 is attached to the rotary shaft 10 in such a manner that it will be slidably moved in the axial direction by means of a key groove 18 formed linearly in the axial direction in the rotary shaft 10 and will be rotated integrally with the rotary shaft 10 when the rotary shaft 10 moves in the axial direction therefore the cam 12 tends to move similarly a positioning member 19 which is fastened to the frame 15 however prevents the cam 12 from producing an axial motion in conjunction with the rotary shaft 10 thus the cam 12 is allowed to produce a mere rotary motion in conjunction with the rotary shaft 10 the cam 11 actuates the plunger 13 of the plunger pump 6 and the cam 12 actuates the plunger 14 of the plunger pump 7 on the portion of the rotary shaft 10 which protrudes from the frame 15 there is provided a centrifugal governor 20 which comprises a v shaped link mechanism 21 and weights 22 placed at the tips of the link mechanism one end of the link mechanism 21 is fastened to the leading end of the rotary shaft 10 and the other end thereof.