PURPOSE: To obtain a circuit which operates a timing conversion without using an elastic store when the frequency of an input clock is the same as that of an output clock.

CONSTITUTION: A transmission clock and a clock obtained by inverting the transmission clock are inputted to a selecting circuit 14. A flip flop 15 latches transmission data by the output clock of the selecting circuit 14. A clock phase comparator circuit 22 compares the phase of the output clock of the selecting circuit 14 with the phase of a reception clock, and instructs the selecting circuit 14 to select the clock for allowing the output of the flip flop 15 to satisfy a timing regulation at a variable delay circuit 19.