A light emitting device includes a semiconductor laser, which oscillates in a single longitudinal mode, formed above a semiconductor substrate, a first heater, which controls a temperature of the semiconductor laser, provided near the semiconductor laser, a gain unit, which amplifies a beam outputted from the semiconductor laser and outputs an amplified beam, formed above the semiconductor substrate, a second heater, which controls a temperature of the gain unit, provided near the gain unit, and a second harmonic generation element, which converts the amplified beam outputted from the gain unit to a second harmonic light and outputs the second harmonic light.