PURPOSE: To facilitate digital IC processing and miniaturization with less jitter by providing a reference clock generating circuit, a switch circuit, a frequency divider circuit, a counter circuit and a preset data output circuit on the variable device.

CONSTITUTION: Since a control signal GS from a counter circuit 23 makes a switch circuit 22 nonconductive for a prescribed period decided by a preset data PSO, the switch circuit 22 extracts a prescribed number of reference clock signal pulses CKST. The degree of a change in the clock signal CKT outputted from the switch circuit 22 is adjusted depending on the extracted pulse number. Since the clock signal is changed without using a voltage controlled oscillator(VCO), jitter is reduced and digital IC processing and miniaturization are facilitated.