To provide an optical signal generator that generates optical signals with a plurality of formats to the same input signal.

The optical signal generator includes a branch section 20, a first modulation section 30, a second modulation section 40, a signal switching section 50, and a multiplex section 82. The branch section branches an optical pulse train into a first pulse train and a second pulse train. The first modulation section adds the first pulse train with either of ON/OFF modulation and phase modulation according to the intensity of the first data signal when the first pulse train and the first data signal are input, and then generates a first modulation signal. The second modulation section adds the second pulse train with either of ON/OFF modulation and phase modulation according to the intensity of the second data signal when the second pulse train and the second data signal are input, and then generates a second modulation signal. The signal switching section performs pulse delay and phase adjustment to the second modulation signal according to a modulation switch signal. The multiplex section mixes the first and second modulation signals to generate an optical modulation signal.