PURPOSE: To realize a direct detection for the pinholes of the packaged article by giving a comparison between the refractive index of the air and the gas leaked out of the packaged article installed in the vacuum box.

CONSTITUTION: Packaged article 2 is stored into vacuum box 1 with airtightness secured via packing 3, and then the decompression is given via vacuum pump 6a. As a result, the inorganic gas leaks out of article 2 containing the pinholes, if any. Then the air containing the gas is led into gas room 8 within interference gauge type gas refraction meter 7. After stopping the decompression, an equal pressure level is secured between room 8 and air room 9 by pump 6b and via vacuum gauges 5a and 5b. Then the beat pattern caused by the difference of the refractive index between rooms 8 and 9 is detected at light reception part 11 via the light of light source 10 and reflector plate 12. And the shift of the beat pattern is converted into the electric signals to be then delivered in the form of the signal alarming the existence of the pinhole.