PURPOSE: To prevent the gaseous discharge of material to be measured by specifying the wavelength of one laser light as the laser light in sub-nanosecond in the two laser light beams used.

CONSTITUTION: Two laser light beams are emitted from a dye laser amplifier 24 and a dye laser 28 at the same timing on a lens 30. Of the two laser beams, the pulse width of one laser light beam is in a picosecond range and the angular frequency is ω1. The other laser light beam has the pulse width in a nanosecond range and the angular frequency of ω2. The emitted two laser light beams, which are condensed with the lens 30, are condensed on a material to be measured H. Thus, the coherent anti-Stokes' Raman scattering spectroscope (CARS) signal (g) is outputted. At this time, as the pump light (e), the light having the pulse width in the picosecond range and the large energy is used. As the Stokes' light (f), the light having the pulse width in the nanosecond range and the small energy is used. Therefore, gaseous discharge does not occur, and the CARS signal having the strong energy is obtained.