PURPOSE: To realize a circuit oscillated in itself synchronously with a signal inputted externally by constituting the title circuit with a control circuit outputting selectively a feedback signal with a control signal and plural inverter circuits in cascade connection receiving an output signal of the control circuit and supplying an output signal to a feedback signal input terminal.

CONSTITUTION: The circuit is provided with a NAND circuit which realizes a function united an inverter of a ring oscillator and a control circuit generating a control signal by using a control signal input signal line 100 and a feedback signal line 105 as input lines and inverters 12-15 connected in cascade with signal lines 101-104 for constituting the ring oscillator. Moreover, a circuit 16 to be synchronized is a circuit to be synchronized by a signal of a feedback signal line 105. Thus, a clock signal generating circuit oscillated in itself synchronously with the signal inputted externally is realized.