A semiconductor laser is for generating colored light. The semiconductor laser oscillates in a longitudinal multimode. A width of a wavelength band with an intensity equal to or more than −20 dB relative to a peak intensity in a spectrum distribution of output light is equal to or less than 15 nm. A light source device may include The semiconductor laser; a wavelength estimating device configured to estimate a wavelength λ of light from the semiconductor laser; and an emission-light intensity setting unit configured to set an emission light intensity of the semiconductor laser in accordance with an estimation result by the wavelength estimating device.