PURPOSE: To increase a motor driving voltage by composing a current mirror circuit of a power transistor and a small signal transistor, and obtaining a control signal by a current detecting resistor connected in series with the small signal transistor.

CONSTITUTION: A current monitoring small signal transistor QS1 is connected in parallel with the emitter and the base of a power transistor QP1, and the collector of the transistor QS1 is connected to the cathode of a current detecting resistor R1. When a voltage across the R1 becomes larger than a reference voltage Vref of a comparator C1, it operates to limit a current of the output (a) of a signal controller C2 by the output C1out of the comparator C1. Thus, a current flowing to the base, the collector of the transistor Q1 and a load current flowing through the base, the collector of the transistor QP1 are both limited.