PURPOSE: To easily detect the pin hole, etc. of a sealed package body by providing an air-gap part on a part of an electric discharge detecting circuit, and detecting the electric discharge of the air-gap part.

CONSTITUTION: Between both terminals of a high voltage power source 11, discharge electrodes 13, 14 placed the sealed package body 12 of a body to be inspected between them, and a discharge detecting circuit 15 are connected in series, and also in a part of this detecting circuit 15, an air-gap part 16 is formed. In this state, when the sealed package body 12 is placed between the discharge electrodes 13, 14, and a high voltage is applied between both the electrodes 13, 14 from the high voltage electric source 11, when a defective part such as a pin hole, etc. exists in the sealed package body, a discharge is generated between both the electrodes 13, 14, the high voltage is all applied to the air-gap part 16 of the detecting circuit 15, the air-gap part 16 also generates a discharge, and a closed circuit is formed by a spark or an arc. Accordingly, by detecting the discharge of this air-gap part 16, the existence of a defective part such as a pin hole, etc. of the sealed package body 12 can be detected easily.