To obtain a test circuit for a clock generating circuit that can perform sampling accurately equivalent to modulation cycles to shorten a measurement period and conduct an accurate function test of down-spread control as one modulating function of a spectrum spread clock generator (SSCG) by accurately testing a center frequency.

A comparator 21 converts an analog modulated wave signal Sm from a modulated wave generating circuit 16 into a digital signal Sd and outputs it, a counter 22 counts cycles of a clock signal So outputted from the clock generating circuit according to the digital signal Sd, and a comparing circuit 25 compares the count value with a specification of the center frequency of the clock signal So set in a specification memory 24.