PURPOSE: To obtain an airtightness testing machine checking whether a hole is present in a wheel rim for a vehicle obtained by melting.

CONSTITUTION: An internal vol. part B formed from an upper plate Ss, a lower plate Si and the cylinder wall Cc of the wheel rim connecting both plates is filled with a liquid from a tank A by a filling pipe Tc. The liquid filling the internal vol. part B to overflow the same goes toward an upper container through an overflow pipe Ts and a differential pressure gauge M is connected to the overflow pipe Ts. An airtight chamber Ct is formed between the outside of the wheel rim and a cylinder Cs to be filled with high pressure gas. If the wheel rim has a leak hole, the inflow of air from the airtight chamber Ct to the internal vol. part B is generated to be capable of being detected as the fluctuations of the differential pressure gauge M.