PURPOSE: To provide a small-capacity inverter, by reducing a restarting time after an instantaneous stoppage of input power and reducing a rush current at the restarting.

CONSTITUTION: An instantaneous stoppage restarting apparatus detects a power- return state and restarts an inverter(INV) after an instantaneous stoppage of input power (AC) for a synchronous motor driving inverter(INV). The instantaneous stoppage restarting apparatus includes a frequency detecting means 100 for detecting a frequency at a terminal voltage of the synchronous motor(SM) when the input power (AC) is stopped, a phase difference detecting means for detecting a phase difference between a terminal voltage of the synchronous motor(SM) and an output voltage command value of the inverter (INV), and synchronously control and restarting means 300 and 400 for making the terminal voltage of the synchronous motor(SM) in agreement with the phase and frequency of the output voltage command value of the inverter(INV) on the basis of the output signals from the detecting means 100 and 200, and restarting the inverter(INV) on condition that the synchronism is completed after the return of the input power (AC).