PURPOSE: To reduce rush-in current generated due to floating capacity of power line by providing an opening/closing means and a coil in series between a power source and a load.

CONSTITUTION: An interlock switch 4 opened or closed in association with the mechanical operation of device is inserted in a power line 3 composed of harness or the like positioned between a power supply 1 and a load 2, and in the vicinity thereof a coil 11 is positioned. At the output portion of the power supply 1, a capacitor C1 is arranged and in a load 2, a capacitor C2 is arranged. In one embodiment according to this invention, a load 5 is connected to the power line upstream of the switch 4, and a capacitor C3 is provided. A capacitor C4 shows the floating capacity of power line positioned upstream of the switch 4 while a capacitor C5 shows the floating capacity of power line positioned downstream of the switch 4. When the switch 4 is disposed on a printed circuit board 12, it is desirable that the coil 11 is on the same board. With this constitution, all rush-in current caused by closure of the switch 4 can be reduced.