Abstract: A nonlinear element provides a nonlinear effect to light output from a pulsed laser source. Remaining light component having the oscillation wavelength of the pulsed laser source is attenuated when the light is split by a dichroic mirror. The divided light is subjected to pulse stretching by a fiber, and is combined by a multiplexing element. The light thus combined is irradiated to a target object S. The light transmitted through the target object S is received by a photoreceiver. The output signal of the photoreceiver is converted by a calculation unit into a spectrum.