To prevent the abnormal increase of the output voltage of a linkage inverter, etc., before a linkage protecting apparatus is operated, by inhibiting based on the sensing of its overvoltage through using a gate blocking signal its drive signal from being fed from a driving circuit portion to it, and by stopping immediately its output.

An overvoltage sensing and controlling portion 31 senses the instantaneous overvoltage of the AC output voltage of a linkage inverter 1 by an overvoltage sensing means formed out of an overvoltage judging portion 31b. Setting based on this sensing of the overvoltage a drive inhibiting means formed out of a latch circuit portion 31c, a gate blocking signal Sg is outputted from the drive inhibiting means until it is reset at a next time to bring an AND-gate portion 30b into OFF-state. Thereby, stopping instantaneously the output of the linkage inverter 1 when its output voltage is increased suddenly, the overvoltage of its output voltage can be prevented surely before a linkage protecting apparatus is operated.