PURPOSE: To prevent the fluctuation of an oscillated frequency to be caused when the temperature is decreased or increased including a compensation code conversion temperature by varying the output of a compensation code to the same temperature depending on the rise and fall of the temperature.

CONSTITUTION: A comparator 9 compares a digital signal at present with a digital signal outputted from an address register 6 at a preceding compensation stored in a storage device at a controller 9 provided with a storage device such as a RAM and an arithmetic register or the like, discriminates it that the temperature is changed in the increasing direction or in the decreasing direction when the both are different, and when the temperature rises, a compensation code corresponding to the temperature at that time is outputted to a ROM 7 and when the temperature is changed in the lower direction, the compensation code corresponding to the preceding temperature is outputted. Thus, the fluctuation of the frequency at each occasion is waded and a stable oscillating frequency is obtained.