PURPOSE: To eliminate mamfunction due to erroneous operation by detecting the supply voltage level for a logic circuit and performing short circuit control of a surge current limiting resistor automatically through relay contacts thereby eliminating manual operation when a package is inserted or removed.

CONSTITUTION: A package including a hot line inserting/removing circuit is inserted through a connector into a DC power supply. When the charging voltage of a capacitor C1, exceeds the sum of Zener voltage of Zener diodes Z1, Z2 and the base.emitter voltage of a PNP transistor Q, the PNP transistor Q is turned ON. Consequently, a relay RL is driven to make the contact r1 thereof thus driving a thyristor SCR. Subsequently, a surge current limiting resistor R1 is short circuited and the thereby the output voltage from a DC power supply is applied, as it is, on a logic circuit. According to the invention, malfunction due to erroneous operation can be eliminated.