To protect a circuit from overheating and overcurrent by arranging a current fuse and a temperature fuse which short-circuits when overheated, in series between input terminals connected to a power line and arranging output terminals before and after the temperature fuse so that the circuit to be protected and temperature fuse may be arranged in parallel with each other.

An overheating and overcurrent blocking unit constituted by combining a current fuse 8 with a temperature 1 is arranged between an AC power source 10 and the circuit 9 of an AC adapter, etc. The temperature fuse 1 is constituted in such a way that, only when the fuse 1 reaches a prescribed temperature, counter electrodes comes into contact with each other and, at normal time, the fuse 1 is maintained in a nonconductive state. When the fuse 1 becomes conductive, the current fuse 8 is burnt out by an overcurrent flowing to the fuse 8. Therefore, the circuit 9 can be protected from overheating and the overcurrent and, accordingly, the malfunction of the circuit 9 can be blocked and the reliability of the circuit 9 can be improved.