PURPOSE: To realize an inexpensive and accurate temperature measurement, by sealing a crystal resonator excited to vibrate and a previously pressurized inert gas up into a pressure resistant container and closing it.

CONSTITUTION: A crystal resonator 2 given a natural resonance frequency and further, with an electrode 2a arranged for applying an exciting voltage from outside and for temperature detection is mounted on a holder 3 as exposed in a pressure resistant container 1. The pressure resistant container 1 is provided with a stop valve 4 to seal an inert gas 5 thereinto at a specified pressure and then, close it so that the container 1 is sealed up. When the external pressure for stopping the vibration of the crystal resonator 2 and the temperature of the gas 5 when sealed in are known, the gas 5 to be sealed can be determined by a simple proportional calculation by determining the temperature to be detected.