PURPOSE: To prevent a large current from flowing in a relay when a power source is turned on.

CONSTITUTION: A relay drive section 3 drives a relay 4 at various timing set by a relay action timing setting section 1 based on the zero cross point at the rising time of the voltage wave-form detected by a voltage wave-form rise detection section 2. A relay action detection section 5 detects the time when the contact of the relay 4 is turned on. An optimum action timing selection section 6 detects/compares the current value when the contact is turned on at each action timing and selects the action timing indicating the minimum current value as the optimum action timing and stores it in an optimum action timing storage section 7. When the relay 4 is operated thereafter, it is driven at the optimum action timing to reduce the rush current.