Abstract: A protection apparatus for a transistor inverter including a detecting circuit connected to a logic circuit detecting the base current and the collector-emitter voltage of a pair of transistors in the inverter to be protected. A logic circuit performs a logical operation on a binary signal based on the base current of one of the transistors and the collector-emitter voltage of the other of the transistors in the pair. When a short circuit in either one of the transistors is detected, the logic circuit operates a protective thyristor which causes a short circuit current to flow through fuses connected to the transistors, thereby electrically cutting off the transistors by the blow out of the fuses.