PURPOSE: To obtain sure oscillation of a control clock and a stable oscillation rising characteristic.

CONSTITUTION: The device is provided with an oscillation circuit 4 generating a control clock for the integrated circuit and a voltage changeover switch 3 selecting a voltage V3 applied to the oscillation circuit 4 to a power supply voltage V1 or a prescribed voltage lower than the power supply voltage V1. At application of power, the power supply voltage V1 is applied to the oscillation circuit 4 and a prescribed voltage lower than the power supply voltage V1 is fed to the oscillation circuit 4 after lapse of a prescribed time. Thus, the energy required for the oscillation is sufficiently applied at application of power and sure oscillation and a stable oscillation rising characteristic are obtained. Furthermore, power consumption is suppressed after lapse of a prescribed time when the oscillation is made stable and the oscillation frequency characteristic independently of the power supply voltage V1 is obtained.