To accurately adjust temperature of a wavelength conversion element performing wavelength conversion of a laser beam.

A laser beam source device 12 is provided with a semiconductor laser array 20, an optical wavelength conversion element 30 and a reflection mirror 40. A thermistor 35 and a heater 37 are connected to the optical wavelength conversion element 30 and a temperature control circuit 70 controls the heater 37 based on the temperature measured by the thermistor 35 to adjust temperature of the optical wavelength conversion element 30. A light shielding plate 50 shielding an unwanted laser beam LB3 is disposed between the semiconductor laser array 20 and the optical wavelength conversion element 30. Thereby, the thermistor 35 is prevented from being directly or indirectly irradiated with the unwanted laser beam LB3.