A light transmission unit (1) is provided with: a light phase modulator (131) for phase modulating continuous wave light; a light intensity modulation means (132) for pulse modulating the phase-modulated light to generate transmission light; a first signal generating means (133) for generating a pulse-modulated drive signal, which has periodically repeating on and off periods, to drive the light intensity modulation means (132); and a second signal generating means (134) for generating a sawtooth wave drive signal to drive the light phase modulator (131), said sawtooth wave drive signal having a constant period and an amplitude that is equivalent to an integral multiple of the drive voltage necessary for acquiring a phase of modulation of 2π at the light phase modulator (131).
