PURPOSE: To realize accurate measurement in a short time without dismantling the component by observing the noise signal spectrum of receiving signal obtained from an output terminal when a pseudo-signal is inputted to the input terminal of a high frequency device.

CONSTITUTION: A pseudo-signal generation means 2 generates a pseudo-signal having power corresponding to 60% or above of the rated current of a circulator 1, for example. When it is fed to the transmission terminal of the circulator 1, the pseudo-signal is outputted to an antenna terminal and terminated and consumed by a dummy load 3. A part of the pseudo-signal inputted to the circulator 1 is attenuated and outputted to the receiving terminal thereof. A receiving filter 4 removes signal of undesired bands and a low noise amplifier 5 amplifies a signal appearing at the receiving terminal by 72 dB, for example, before feeding to a spectrum analyzer 6. When the circulator 1 is oscillated using a vibrator, relatively small crack and the like are rendered conspicuous positively and detected easily.