PURPOSE: To enable a prediction of an ink drip flying state without assembling an ink jet head, by receiving an acoustic wave from a vapor bubble generated in a liquid, correcting a propagation strain in a medium to which the acoustic wave is transmitted and a receiving system, and calculating an original acoustic wave of the vapor bubbles.

CONSTITUTION: An acoustic wave of a vapor bubble 104 generated in a liquid by a thermal ink jet head 106 is received by a sensor 108 and waveform-shaped by a band filter 122 and an amplifier 124. The output from an acoustic wave detection system 120 is inputted to an acoustic waveform analysis system 130. A detection waveform V in a frequency area is calculated by a high-speed Fourier conversion circuit 132, it is divided by a predetermined synthetic transfer function G by a division circuit 134, and an acoustic wave P102 in the frequency area is calculated. Furthermore, P is converted by an inverse high-speed Fourier conversion circuit 136 to obtain an acoustic wave P102 in a time area. The acoustic wave P is inputted to an acoustic energy analysis system 140, and then an acoustic energy is obtained. In a volume velocity conversion system 137, a volume velocity is obtained.