To inspect leakage of a liq. without breaking a product and to shorten time for inspection by providing a process wherein a paper pack container filled with the liq. is arranged in an inspection container, which is then hermetically closed by closing the inspection container and after the inside of the inspection container is made vacuum to a specified pressure, the vent hole of the inspection container is closed and change in pressure in the inspection container is measured.

In the first process, a paper pack container 12 is arranged in an inspection container 13 and a direction control valve 23 is switched and a cylinder 24 is started and the lid 16 of the inspection container 13 is closed to make an hermetically closed condition. In the second process, a pressure sensor 14 is started to start measurement of pressure in the inspection container and a shut-off valve 18 is switched and air in the inspection container 13 is vented for a specified time by means of a vacuum pump 11 connected with the inspection container 13 to make the inside of the inspection container 10 vacuum. When the vacuum does not reach a specified pressure, inspection of the paper pack 12 is finished. In the third process, whether there exists furthermore a very small gap in the paper pack container 12 being brought to at most the specified pressure is measured by means of the pressure sensor 14 to judge leakage of the liq.