PURPOSE: To eliminate the change of position of an annular slider of a fuel injection pump for an internal combustion engine caused by the axial play of a speed adjusting lever mechanism so as to achieve the slightest possible change of fuel injection quantity by extremely simple means.

CONSTITUTION: A pump piston 10 operating in a pump cylinder 11 is driven to move reciprocally and rotationally at the same time. The pump piston forms a pump chamber 13. A passage 29 escaping therefrom extends through the outer periphery of the pump piston. The opening and closing of an opening portion thereof is controlled by an annular slider 28 axially movable with respect to the pump piston. The annular slider is acted by a speed adjusting spring mechanism 34 of a governor. The annular slider is secured by a guide portion 62 with slight radial play.