The laser device includes: a seed light source that outputs seed light; a pumping light source an amplification optical fiber as the amplifier that amplifies the seed light with an element pumped by the pumping light source; a monitor unit that is provided between the seed light source and the amplification optical fiber, and monitors the intensity of the light output from the amplification optical fiber; and a light source controller that controls the seed light source. In this laser device, when the light input to the monitor unit has an intensity equal to or higher than a predetermined intensity while the seed light is not input to the amplification optical fiber, the light source controller forces to output the seed light from the seed light source.