To realize a clock signal generating circuit that can generate a clock signal with an optional frequency division ration.

The clock signal generating circuit that applies frequency- division to a system clock, is provided with an adder that sums external input data and a preceding sum result and a storage means that stores the result of sum of this adder synchronously with the system clock and supplies the output to the adder as the preceding sum result, and extracts the most significant bit of the output of the storage means as a clock signal.