PURPOSE: To prevent the overload against a motor by connecting a transistor between circuits which drive the starting motor and driving the motor at a point in time when the transistor has reached a saturation current.

CONSTITUTION: An engaging switch 2 and a PNP power transistor 8 are connected between a battery 6, a key switch 7 and a starting DC motor 1. The switch 2 has a function to flow a main current to the motor 1, and comprises a main contact 3, a battery connecting terminal 3a, a motor connecting terminal 3b, a suction coil 4 and a holding coil 5. Further, the transistor 8 has a function to operate the main current to be flowed to the motor in a saturation range, and makes it possible to drive the motor in the saturation range.