To detect both of partial discharge of a capacitor for power which is connected with a series reactor and a failure of short-circuit of an element by one current transformer with high reliability and inexpensively.

A current transformer for detecting abnormality 5 in a wide frequency band zone which has detection sensitivity of 10 to 1000 times in a high frequency band zone for detection sensitivity of commercial frequency is inserted into a line connected in parallel of two capacitor element collection 2a and 2b to detect a partial discharge current 4 of a high frequency or a capacitor load current 6b of a commercial frequency. After that, an output signal 4a of the current transformer for detecting abnormality 5 is divided into a high frequency signal and a low frequency signal by a frequency divider 7. This high frequency signal is detected by a partial discharge detector 9, and the low frequency signal is detected by an element short-circuit failure detector 8 which detects a short-circuit failure of the capacitor element.