PURPOSE: To protect a power source equipment from breakdown, when it is connected erroneously with a different type power source, by tripping a non-fuse circuitbreaker if the current flowing through a smoothing capacitor is larger than a specific value.

CONSTITUTION: Power from an AC power source is fed through a non-fuse circuitbreaker 1 and an input power source monitor circuit 3 to a rectifier circuit section 4. Current flowing between the neutral point of smoothing capacitors C1, C2 and source line is detected at a current detecting section 5. If the level of detected current is higher than a specific level, it is judged to be erroneous connection with a different type power source and the non-fuse circuitbreaker 1 is tripped through the input power source monitor circuit 3. A short piece 8 is provided for a current detection line (l), and the short piece 8 is removed when the device is used with high voltage.