PURPOSE: To provide a pre-charge circuit preventing overcurrent at the starting time of pre-charge and also simplifying a circuit element.

CONSTITUTION: A bus 6 is pre-charged with a constant current supplied by a constant current transistor 1 by a first pre-charge transistor 3; the constant current transistor 1 is bypassed to a power source by a second pre-charge transistor 4 after the elapse of a prescribed time; and the bus 6 is raised almost to a power source potential and pre-charged. Overcurrent is suppressed by the constant current pre-charge, and the lowering of voltage due to the constant current source 1 is eliminated through a bypass by the second pre-charge transistor 4 after a prescribed time.