To realize low power consumption by providing a resistive element for converting load current of a first transistor connected with a coil to voltage and detecting it, a second transistor that is connected so as to bypass an input terminal of this transistor and impresses the detected voltage value of the resistive element as an input, and a capacitor in parallel with the resistive element.

A coil Ry of a relay is connected between a collector of a first transistor and a power supply +5 V, and a resistive element 2 is connected between its emitter and a power supply 0 V. A second transistor 3 is connected between the first transistor and the power supply 0 V so as to bypass this, and a capacitor 4 is connected so as to bypass the resistive element 2. Charge voltage of the capacitor reaches an input threshold voltage of the second transistor, the first transistor acts as a low current source, and without change of operation characteristic by change of coil resistance, it rapidly drops from a large value just after turning on to a defined value.