Partial discharge detection method and partial discharge detection device

In a method of determining partial discharge which detects an electromagnetic wave signal, which propagates in metal tank, at a plurality of outer circumferential positions of the insulating spacer with an electromagnetic wave detector; extracts a signal of a frequency band in which a TE11 mode propagates but a TE21 mode does not propagate by utilizing a cutoff frequency from the detected electromagnetic wave signal, with a TE11 envelope detector; and determines a partial discharge by detecting an intensity distribution of outer circumferential electromagnetic waves in the metal tank with an intensity detector from the intensity of the extracted signal with the TE11 envelope detector and the outer circumferential position information of the electromagnetic wave detector, a structure information output unit which outputs inside structure information of the gas-insulated equipment is provided; and the presence or absence of a partial discharge is determined from the intensity distribution of outer circumferenti