To output an optical pulse train of which the repetition frequency has been converted to a lower value substantially without loss.

An optical pulse train conversion apparatus includes: a phase modulation par 21 which subjects an input optical pulse train to phase modulation in accordance with a phase modulation signal; and a group velocity dispersion part 22 which gives group velocity dispersion necessary for a partial temporal Talbot effect to the optical pulse train subjected to the phase modulation to output an optical pulse train of which the repetition frequency has been reduced.