A laser oscillator according to this invention includes a resonator unit, heat exchangers, fans, a resonator temperature measuring unit, and a fan control unit. The resonator unit resonates a laser beam to be output. The heat exchangers are arranged adjacent to the resonator unit and are to be supplied with a cooling liquid. The fans are arranged at least at one of two opposite positions across both the resonator unit and the heat exchangers and generate airflow in one direction, which passes through both the resonator unit and the heat exchangers. The resonator temperature measuring unit measures the temperature of the resonator unit. The fan control unit controls the fans. The fan control unit switches the direction in which air is blown by the fans, based on the temperature of the resonator unit.