Abstract: In a laser having a frequency conversion element or a non-linear optical element such as a second-harmonic generation (SHG) element arranged on an optical axis of a laser light and outputting a frequency-converted laser light, laser incident and emitting faces of the SHG element have such convex form as cylindrical lenses with a common center axis of curvature thereof and orthogonal to the optical axis of the laser light. The SHG element is rotatable about the common center axis of curvature so that an optimum control of phase matching angle is possible. Since the common center axis of curvature of the laser incident and emitting faces of the SHG element is coincident with the rotational axis thereof, an optical axis of a fundamental wave of the laser light source is not deviated when the SHG element is rotated and thus reduction of fundamental wave laser output can be restricted.