A signal multiplexing device includes a selector (1) that selects one of input data (4) and a complementary signal (16), a clock recovery circuit (30a) that adjusts the phase of a recovered clock (7) to the timing of the output signal of the selector (1), and a flip-flop circuit (3) that performs identification/recovery of the output signal of the selector (1) based on the recovered clock (7). The frequency of the complementary signal (16) is an integral submultiple of the frequency of the recovered clock (7). The selector (1) selects the complementary signal (16) during part of the no-signal period of the input data (4).