The invention provides a compact laser light source whose wavelength can be designed freely in a wavelength band in which the semiconductor laser has not been put to practical use by combining an efficient nonlinear optical crystal and high-power semiconductor lasers for optical communication. In one embodiment, the laser light source includes: a first laser for generating a laser beam of a wavelength .lamda..sub.1; a second laser for generating a laser beam of a wavelength .lamda..sub.2; and a nonlinear optical crystal that allows the laser beam of wavelength .lamda..sub.1 and the laser beam of wavelength .lamda..sub.2 as inputs and outputs a coherent beam having a wavelength .lamda..sub.3 of a sum frequency that satisfies a relationship of 1/.lamda..sub.1+1/.lamda..sub.2=1/.lamda..sub.3. The wavelength .lamda..sub.3 of the sum frequency is 589.3.+-.2 nm that is equivalent to the sodium D line.