A laser apparatus includes a heat transfer device having a cooling fin at a temperature lower than that of a heat radiation jacket, and a cooling fan. A controller controls the cooling fan so as to be stopped when temperature detected by a temperature sensor is lower than a temperature reference value and humidity detected by a humidity sensor is higher than a humidity reference value. The controller controls the cooling fan so as to be driven when temperature detected by the temperature sensor is higher than the temperature reference value and humidity detected by the humidity sensor is lower than the humidity reference value.