Abstract: A format converting system includes a first converter which converts an input signal into N parallel signals (N is an integer). Each of the N parallel signals has a bit rate less than that of the input signal. A latch circuit temporarily latches the N parallel signals in accordance with a clock signal and outputs a plurality of latched signals having a number larger than the N. A selector selectively outputs the latched signals from the latch circuit and stuff bits to be inserted in the N parallel signals in accordance with a control signal so that N parallel output signals having the N parallel signal and the stuff bits are output from the selector. The stuff bits are used for converting a frame format of the input signal into a different frame format.