Abstract: A control rack for driving the fuel injection quantity control member of an injection pump which supplies fuel to a diesel engine is driven by a magnetic actuator mechanism. The position of the control rack is transmitted to a position sensor via a tie bar which is pivotally supported by a support shaft. The sensor detects a signal corresponding to an actual amount of fuel to be injected. The support shaft is supported by a control member which is pivotally supported. The control member sets a reference position of the support shaft, and hence, sets the relative positional relationship between the control rack and the position sensor. A portion of the control member extends outside a housing, so that the reference position of the tie bar can be corrected outside the housing. The actuator mechanism is controlled by an instruction from a control circuit which calculates an optimal amount of fuel to be injected.