To provide a pseudo-combustion vibrator which has proper response characteristics, which can detect vibration force by contacted part to an engine, having a small vibration part, and capable of vibration not only a piston top surface but also the under surface of a cylinder head, simultaneously.

This vibrator comprises a vibration part (5), comprising a piezoelectric element (11) and a force sensor (13) in a combustion chamber (4a) of the piston (4). The vibration signal of a cylinder pressure waveform for vibration of the bottom of the combustion chamber (4a) and the under surface of the cylinder head to vertical direction of the piston is applied to the piezoelectric element (11) via a drive amplifier (32) from a personal computer(31). Then, this output signal from the force sensor (13) is set as the combustion vibration force, when the vibration is performed; and a spectrum analyzer (33) computes the combustion vibration force/sound power as a SA response characteristics, by inputting each output signal at the vibration of a plurality of the vibration sensors and the force sensors (13) attached around the engine.