PURPOSE: To obtain a quartz oscillator that maintains high accuracy with exclusion of other temperature detecting elements, by sealing airtight a resistance heat generator and a quartz oscillating bar and switching on and off of the electric conduction to the resistance heat generator in accodance with the frequency of oscillation.

CONSTITUTION: A quartz oscillating bar 1 is joined to lead wires 2 and 3 by means of a junction material, etc. and then sealed airtight to an airtight container 4 of glass, etc. A heat generator thin film 5 of a metal, etc. like Ni-Cr, etc. having a high resistance value is provided on the inner surface of the container 4 to be connected to lead wires 6 and 7 piercing through the container 4. Then the lead wires 2 and 3 of a quartz oscillator 8 having such constitution as mentioned above are connected to an osicllating circuit 9 to cause the oscillation. The frequency of oscillation is compared with the value set by a setting circuit 11 through a comparator 10. Thus the ON/OFF of the electric conduction is controlled to the thin film 5 for a heating power supply 12 which is connected to the lead wires 6 and 7 of the film 5.