PURPOSE: To prevent noises during solenoid driving by using a triangular wave shaped signal giving a small amount of variations in attraction during the operation time of a plunger as a driving signal for a solenoid to decrease increments of a voltage and a current at the time of completion of operation of the plunger.

CONSTITUTION: The collector of a switching transister Tr2 in a solenoid driving system is connected to a DC voltage V giving a solenoid the maximum suction (f) and the emitter is connected to one end of a solenoid coil (l). Furthermore, the other end of the coil (l) is grounded and the base of the transistor Tr2 is connected with a triangular wave generator G outputting a triangular wave- shaped signal in response to a driving command signal (l) from the solenoid. When the solenoid is driven, the coil (l) is applied with a triangular wave-shaped voltage (a) giving a small amount of variations in suction of the plunger from a circuit G to make suction (current) (b) of the coil (l) triangular shaped and reduce increments of a voltage (a) and a current (b) at the time of completion of operation (c) of the plunger.