The wavelength converting device comprises a BBO crystal of length L along the propagation direction of incident light C and a filter transmitting only light E by second harmonic generation. The BBO crystal is composed of 10 pieces of crystal equally divided in parallel planes along the propagating direction of the light. Each crystal piece has a crystal axis respectively and is positioned with the crystal angle satisfying a phase matching condition for second harmonic generation and so that the adjacent crystal axis is oriented in a crystallographically different way. The acceptance angle φ in the insensitive direction becomes the same as the acceptance angle ϑ in the sensitive direction; therefore, there is no necessity for gathering light to an oval shape, and maximum conversion efficiency can be obtained by gathering light with a conventional spherical lens.