PURPOSE: To make it possible to take proper measure and to prevent accident from spreading to a large hazard by confirming a partial discharge generated place by the detection signal, the discharge charge amount and the generation frequency at the time of the generation of partial discharge.

CONSTITUTION: When partial discharge is generated in a gas hermetically sealed matrix wire 10, a minute current due to discharge is taken out by a current detection terminal 4 embedded in an insulating spacer 2. In an operation apparatus 7, the content of the mutual relation of the output of an AD converter 6 and the false obstacle, the discharge charge and the generation frequency stored in a memory apparatus 9 is taken and the generation place of partial discharge is determined by one large in mutual relation. The operation result is displayed by a display apparatus 8.