PURPOSE: To detect incorrect inner pressure regardless of temperature by detecting the temperature of a hermetically sealed container at the time of hitting test, correcting the frequency at the time of hitting test based on the variation of acoustic frequency corresponding to the difference between the detected temperature and a reference temperature, and then comparing the corrected frequency with a set frequency.

CONSTITUTION: When a can arrives at a droplet removing unit 6, a sensor 8 detects the can and an I/O control circuit 17 operates an exciter 23 and an exciting coil 4 to shake off the solution from the rear side of the wall of the can. When the can arrives at a hitting test position, a sensor 9 detects the can and the I/O control circuit 17 operates an exciter 21 and an exciting coil 2 to produce a hitting test sound. A microphone 3 detects the sound which is subjected to data processing for determining a hitting test frequency. Furthermore, a frequency correction value is determined based on the temperature of the can fed from an infrared radiation thermometer 5 and a reference temperature fed from a setting/displaying unit 11 in order to correct the hitting test frequency. The corrected hitting test frequency is compared with preset upper and lower limit values and a reject signal is outputted for a can deviated from that range.