A clock transfer device is designed to perform long-distance transfer of a reference clock, which is generated based on a high-precision frequency standard, toward a remote place. The clock transfer device includes a first mode-locked laser for generating a first optical pulse train having a first repetition frequency and a first wavelength, and a second mode-locked laser for generating a second optical pulse train having a second repetition frequency and a second wavelength. The first optical pulse train is introduced into a resonator of the second mode-locked laser via a wavelength multiplexing coupler so that the second repetition frequency is passively synchronized with the first repetition frequency; then, the second optical pulse train is transmitted via a single mode fiber.