A laser light source 1 is provided with an output mirror 11, a laser medium 12, a light beam diameter adjuster 13, an aperture 14, a reflection mirror 15, a drive unit 21, and a control unit 22, and outputs laser oscillation light 31 from the output mirror 11 to the outside. The laser resonator is configured so that the reflection mirror 15 and the output mirror 11 are disposed so as to be opposed to each other with the laser medium 12 placed therebetween. The reflection mirror 15 is configured such that it gives amplitude or phase variations to respective positions in the section of a light beam when the light is reflected, and the reflection mirror presents a amplitude or phase variation distribution in accordance with control from the outside, and determines the transverse mode of the laser oscillation light 31 based on the amplitude or phase variation distribution. Thus, a laser light source capable of easily controlling the transverse mode of the laser oscillation light can be realized.