PURPOSE: To obtain a sensor suitable to a digital system by measuring the frequency or period of counting operation through the counting operation.

CONSTITUTION: A vibrating piece 1 is formed by joining plates 11 and 12 made of materials having different coefficients of heat expansion with each other and its one end is joined with holders 3 and 4 and fixed to a base 2. Further, a weight 5 is fitted to the other end of the vibrating piece 1. Further, a piezoelectric element 6 for driving and a piezoelectric element 7 for detection are provided. Vibrations of the vibrating piece 1 are detected by the element 7 and converted into an electric signal, which is amplified 8; and the output of the amplification is applied to the element 6 to drive the vibrating piece 1. This feedback allows the vibrating piece 1 to oscillate continuously at its resonance frequency. The output voltage signal of the amplifier 8, on the other hand, is led out and its frequency or period is measured by a counter, so that temperature is known from the measured value.