To provide a hot line inserting/extracting circuit and a single weight drive system in which a load unit can be carried easily by not only suppressing an inrush current at the time of starting charging of a smoothing capacitor but also discharging residual charges after extraction of the load unit.

An inrush current I to a capacitor C1 is suppressed immediately after fixing a load unit 5 to a power supply by providing a relay 53 for switching a switch SW and a power supply actuating a relay for delaying the switch and power consumption through a resistor R1 is prevented at the time of supplying power to a load by switching the switch SW. A threshold voltage comparing/deciding section 52 for comparing the potential on the low potential side of the capacitor C1 with a threshold voltage E0 can determine extraction of the load unit 5. Residual charges in the capacitor C1 is consumed (discharged) by a resistor R2 by switching the switch SW based on the determination.