To provide a fuel injection pump-driving device capable of reducing a tooth hitting sound which occurs between a cam gear disposed on a camshaft and the drive gear transmitting an engaging power thereto even in the case that only one cam is disposed on one camshaft.

In a cam for lifting a plunger tappet having a return spring against the resilient force thereof, a cam profile is formed in such a way that a minute torque acts on the cam in the direction same as that of rotation of the camshaft by a pressing force acting on the cam from the plunger tappet when starting to lower it. Thereby, the cam gear and the drive gear are loosely abutted on each other in the tooth face of opposition actuation side opposite to that of drive side in which both gears abut on each other when the plunger tappet is lifted.