To enable precise and quick and measurement of the volume of an engine combustion chamber having a complicated shape, in a dried state as it is, in the manufacturing process of engines.

In the apparatus, a reference vessel is mounted on the combustion chamber of a transposed engine block and an alternating volume change is applied differentially to the inside spaces of the reference vessel and the combustion chamber by a speaker. The amplitude ratios of pressure changes for the two inside spaces that occur at the time are measured, and then the volume difference between the combustion chamber and a reference vessel can be determined from the ratio of the reference vessel mounted on the combustion chamber and the ratio of the reference vessel mounted on the standard vessel.