| 摘要 |
PROBLEM TO BE SOLVED: To prevent the deterioration in image quality occurring in a fluctuation of the intensity of the beam emitted from a beam source by a temperature change of the beam source. SOLUTION: A pipe 66 is arranged to pass the inside of a laser stage 65 arranged between a laser beam source unit 51 including the laser beam source 51a and a base 50a of a housing 50. A fan 81 and an electric heater 82 are connected to the pipe 66. If a proper quantity of air is made to pass a laser stage 65 by driving the fan 81 and/or the electric heater 82 in accordance with the temperature detected by a thermistor 62 arranged within the laser beam source unit 51, the temperature of the laser beam source unit 51 is kept within the prescribed temperature range.
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