PURPOSE: To improve valve opening-and-closing response characteristics by conducting small currents corresponding to the holding of the state of attraction through an electromagnetic coil when reaching a stroke end corresponding to the full admission of a valve of an armature attracted through the excitation of the electromagnetic coil is detected.

CONSTITUTION: When the pulse of valve-opening time τ arithmetically operated by a last arithmetical circuit 12 on the basis of the quantity of air sucked, etc. is inputted to a control circuit 7, a transistor Tr2 is turned ON while an output from a FF1 is inverted through a trigger circuit 15, and transistors Tr3, Tr4 are turned ON. Consequently, the electromagnetic coil 3' of the fuel injector is supplied with large currents through a parallel circuit of resistors RL1, RL2. After the conduction is started, pulses of fixed width are generated from a one- shot circuit 19 through a differentiation circuit 17 and a waveform shaping circuit 18, and the FF1 is reset by a trigger circuit 20 at the rise time of pulses. Accordingly, Tr3 and Tr4 are turned OFF, and currents limited by RL1 are conducted through the electromagnetic coil 3'.