PURPOSE: To reduce the installation area the title system and its cost by providing a monitor/controller for monitoring input voltage of a rectifier and commanding stop/drive of an inverter according to whether power is interrupted or not thereby reducing the capacity of battery and power supply and suppressing increase of the capacity of rectifier.

CONSTITUTION: A monitor/controller 4 receives voltage from AC input side of a rectifier 1 and provides a start or stop command to an inverter 2 according to the state of the rectifier 1. Since a battery 3 is employed as power supply, it is not influenced by interruption or recovery of AC input. AC input voltage for the rectifier 1 is fed to the monitor/controller 4 according to a monitoring/ controlling procedure in order to judge power interruption. In case of power interruption, a timer starts counting of time and upon judgement of time up of AC component power interruption guarantee time, the inverter 2 is stopped. Upon recovery of power, an operation restart command is fed to the inverter 2.