Provided is a method for lighting a high pressure discharge lamp capable of increasing the life thereof. The lighting method is as follows. When the time elapse after lighting up the discharge lamp is within a predetermined condition (e.g. 5 minutes or less), constant current control is performed if the lamp voltage is lower than switching voltage (here, a first voltage value V1) and constant power control is performed to maintain the lamp power at a power value W1 if the lamp voltage is equal to or above the switching voltage. After the predetermined condition (5 minutes) is exceeded, the constant power control is performed by lowering the value of the switching voltage from the first voltage value V1 to the second voltage value V2. If the lamp voltage is equal to or above the switching voltage lowered, the lamp power is maintained at power value W1.