PURPOSE: To vary the repetitive period of a function output easily over a wide range, by varying the rate of thinning when a sampled-value sequence is read out of a memory.

CONSTITUTION: In a memory 11, a sampled-value sequence in a prescribed section of a period function is stored. This sampled-value sequence is read out of the memory by address data from an address specifying circuit 15 and a clock signal CK from a clock oscillator 16. This signal CK specifies the read timing of the memory 11 and the timing of the address specifying operation of the circuit 15. The circuit 15 consists of, for example, a counter and is set according to a repetitive period setting code X supplied externally. For the sampled-value sequence in the memory 11, the order of address specification is so set that every (N)th value (N; optional integer) is accessed successively, thereby reading it out as a function output.