To secure stable injection control by restraining injection control accuracy from reducing with the lapse of time caused by abrasion without increasing an engaging pin in a linkage using the balllike engaging pin.

Two planes 17a which are in parallel with each other are formed on one of movable members to be linked, and an engaging pin 22 which is engaged between the two planes 17 is formed on the other movable member. An axis of the engaging pin 22 is in parallel with the two planes. The engaging pin 22 is continuously varied so as to be equal in a distance from an axial center in a circumferential direction and to be decreased in a distance from the axial center at both ends in a axial direction, and a radius of curvature R in the axial direction is made larger than the half (=r) of the distance between the two planes. Accordingly, the dimensional change in a radial direction due to abrasion of the engaging pin 22 can be reduced.