To allow an oscillator which adjusts the control voltage of a voltage- controlled oscillation circuit according to a temperature detected value which is obtained by a temperature sensor to control the oscillation circuit to a constant oscillation frequency from right, after the power source is turned on.

An oscillation circuit 2 is provided with temperature sensors S1 and S2, which detect the temperatures of a vibrator and a transistor(TR), and when feedback control over the oscillation frequency can not be performed by a PLL divider 32, a control voltage which should be inputted to the oscillation circuit 2 according to the temperature detected values V S1 and V S2 of the temperature sensors S1 and S2 and a storaged data in a storage element 4 and inputted to the oscillation circuit for controlling the oscillation frequency of the oscillation circuit 2. Furthermore, when the oscillation frequency of the oscillation circuit 2 can be controlled by the PLL divider 32 by using a reference signal generated by a GPS receiver 30, control data in the storage element 4 are updated by using the control voltage outputted by the PLL divider 32 and the temperature detected values VS1 and VS2 obtained by the temperature sensors S1 and S2.