An angle .beta. between a principal ray of incident light incident on an optical fiber via a lens system and a marginal ray of reflected light nearest to the principal ray of the incident light when the reflected light is the incident light reflected on an entrance end surface of the optical fiber is larger than an angle .theta. between the principal ray and a marginal ray of the incident light. A receiving surface is provided separately from an inner surface of a light-passing hole so that the reflected light is received by the receiving surface. Therefore, the reflected light from the entrance end surface of the optical fiber is prevented from returning to a semiconductor laser light source to thereby attain improvement in stability and high reliability of laser light output of the semiconductor laser light source.