PURPOSE: To prevent a starter from overrun in such a way that even after applied voltage on the starter starting command terminal has been put out, relay contacts between the terminal and the direct current power source are kept opened by a timer circuit.

CONSTITUTION: The starting command terminal 13 of a starter 6 is connected to a relay fixed contact 15 of a protective device 14 and to a battery 1. When a driving contact 3 is turned on, power supply comes into the protective device 14, an alternating current generator 17 generates power, a comparator 26 gives positive input < negative input, and transistors 31, 32 are turned off. Then, when a starter contact 4 is turned on, contacts 15, 16 are turned on, the starter 6 starts up with supplying power to the starting command terminal 13, a capacitor 38 sets to charge, and as frequency of the generator 17 comes to be more than the determined value, the comparator 26 is inverted to give positive input > negative input, transistors 31, 32 are separately turned on and off, the contacts 15, 16 are released, power supply of the starter 6 is stopped.