PURPOSE: To reduce the rise time to reach the reference temperature for the crystal oscillator which stores the crystal oscillator in the thermostatic oven containing the heating part by providing the auxiliary heating part to give the direct heating to the oscillator in addition to the main heating part.

CONSTITUTION: Inner barrel 4 containing heating part 5 inside is stored into outer barrel 6, and adiabator 7 is filled into the space between barrels 4 and 6. Then crystal oscillator 1 is stored within barrel 4. In this case, auxiliary heating part 2, which is formed into the heat barrel type by winding the resistance wire as if it enclosed oscillator 1, is provided. Furthermore, heat-sensitive element 3 consisting of the thermistor or the like is put to oppose to oscillator 1, and the lead wire connected to element 3 is connected to the 1st control circuit 8 connected to part 2 as well as to the 2nd control circuit 9 connected to part 5 each. In such constitution, part 2 is actuated for a fixed time from the make of the power source, and thus the time reaching the reference temperature is reduced. At the same time, the time reaching the steady region of the characteristics can be reduced.