PURPOSE: To improve precision by propagating a surface acoustic wave on the surface of a both-ends held beam formed on the surface of a semiconductor substrate from one end to the other, and detecting oscillations on the basis of a modulated component in the surface acoustic wave after the propagation.

CONSTITUTION: A surface acoustic wave is excited by a transmitting electrode 11 to propagate on the surface of the both-ends held beams 10 and is received by a receiving electrode 12, and the received signal is returned to the transmitting electrode 11 through an amplifier 13, thus constituting a loop type oscillator. The oscillation frequency of this loop type oscillator is modulated according to oscillations of the beam 10. For the purpose, the modulation degree of this oscillation circuit is detected to detect the resonance degree of the beam 10.