A laser device comprising: a plurality of oscillating means configured to oscillate a plurality of laser lights (L 1) being continuous lights and having frequencies different from each other, respectively each of the oscillating means being connected with an optical fiber through which each of the laser lights (L 1) propagates; multiplexing means (12, 13) configured to multiplex the respective laser lights (L 1) oscillated from the respective oscillating means at a predetermined position to generate a multiplexed light (L 2); and phase control means, located between the plurality of oscillating means and the multiplexing means (12, 13), the phase control means being arranged to control the phase of each of the laser lights (L 1) so that a peak in output of the multiplexed light (L 2) repeatedly appears at predetermined time intervals at the predetermined position; and characterised in that the phase control means comprises: a phase difference detecting unit, configured to detect a phase difference between laser lights from the plurality of laser lights (L 1) having frequencies adjacent to each other on the frequency axis and to send information indicating a result of the detection to a signal control unit; the signal control unit, configured to determine phase control amounts of the laser lights having frequencies adjacent to each other to make the phases of the laser lights identical, based on the information indicating a detected phase difference from the phase difference detecting unit, and to send information indicating the determined control amounts to a plurality of phase control units; and each phase control unit of the plurality of phase control units being configured to adjust the temperature of a respective optical fiber from the plurality of optical fibers, based on the information indicating the control amount from the signal control unit, so as to adjust the optical path length of the respective laser light that propagates through the respective optical fiber. a plurality of oscillating means configured to oscillate a plurality of laser lights (L 1) being continuous lights and having frequencies different from each other, respectively each of the oscillating means being connected with an optical fiber through which each of the laser lights (L 1) propagates; multiplexing means (12, 13) configured to multiplex the respective laser lights (L 1) oscillated from the respective oscillating means at a predetermined position to generate a multiplexed light (L 2); and phase control means, located between the plurality of oscillating means and the multiplexing means (12, 13), the phase control means being arranged to control the phase of each of the laser lights (L 1) so that a peak in output of the multiplexed light (L 2) repeatedly appears at predetermined time intervals at the predetermined position; and characterised in that the phase control means comprises: a phase difference detecting unit, configured to detect a phase difference between laser lights from the plurality of laser lights (L 1) having frequencies adjacent to each other on the frequency axis and to send information indicating a result of the detection to a signal control unit; the signal control unit, configured to determine phase control amounts of the laser lights having frequencies adjacent to each other to make the phases of the laser lights identical, based on the information indicating a detected phase difference from the phase difference detecting unit, and to send information indicating the determined control amounts to a plurality of phase control units; and each phase control unit of the plurality of phase control units being configured to adjust the temperature of a respective optical fiber from the plurality of optical fibers, based on the information indicating the control amount from the signal control unit, so as to adjust the optical path length of the respective laser light that propagates through the respective optical fiber. a phase difference detecting unit, configured to detect a phase difference between laser lights from the plurality of laser lights (L 1) having frequencies adjacent to each other on the frequency axis and to send information indicating a result of the detection to a signal control unit; the signal control unit, configured to determine phase control amounts of the laser lights having frequencies adjacent to each other to make the phases of the laser lights identical, based on the information indicating a detected phase difference from the phase difference detecting unit, and to send information indicating the determined control amounts to a plurality of phase control units; and each phase control unit of the plurality of phase control units being configured to adjust the temperature of a respective optical fiber from the plurality of optical fibers, based on the information indicating the control amount from the signal control unit, so as to adjust the optical path length of the respective laser light that propagates through the respective optical fiber.