In an information device which has a laser light source and a non-linear optical crystal for converting the laser fundamental wave light irradiated from the laser light source into harmonic wave light and uses the laser light passing through the non-linear optical crystal, a prism or an optical grating is provided to separate an optical path of the fundamental wave light remaining in the laser light passing through the crystal from an optical path of the harmonic wave light with the purpose of eliminating the fundamental wave light. In another embodiment, a polarization filter is provided to eliminate the fundamental wave light.