A control device for a filling-ratio adjusting pump with at least one displacement space works on the suction-throttle principle with a positive variation in volume of the displacement space or displacement spaces and is intended inter alia particularly for common-rail diesel injection systems. It allows an exact, precise and highly dynamic control of the filling-ratio adjusting pump at low outlay, without the system being impaired by undesirable cavitation. Located on the suction side of the pump is at least one throttling 2/2-way valve (21, 21a, 21b; 134; 51, 52, 53, 54; 81; 103) actuated by pressure difference. Either such a 2/2-way valve can be used for a group of displacement spaces or for the entire pump or a respective valve of this type can be inserted in front of each individual displacement space. The pressure-difference control of the or each 2/2-way valve takes place via an adjusting device (27; 150) which is arranged on the inflow side of the 2/2-way valve and which is designed either as a throttling valve or as a flow-regulating valve.