To enable the inspection during the execution by transmitting a radio wave of directive frequency as the signal, and receiving the radio wave to measure the shield performance, to facilitate the carriage by reducing the weight and the size of a measuring system, and to reduce the cost of the system.

A gun oscillator 12 is used for a transmission element. The reverse flow of the radio wave is prevented by an isolator 13, and the radio wave having the linearity of the transmission frequency of around 10 GHz is transmitted. The received radio wave of 10 GHz is converted into the frequency of around 1.5 GHz by a converter 23. The converted frequency is amplified by an amplifier 25, and inputted in an electric field indicator 3 by a spectrum analyzer capable of coping with the fluctuation of the received frequency to some extent by a cable 26 to measure the shield performance.