Excimer laser apparatus and excimer laser system

The excimer laser apparatus may include a laser chamber configured to contain gas, a pair of electrodes provided in the laser chamber, a power source unit configured to supply a pulse voltage between the pair of electrodes, a gas supply unit configured to supply gas into the laser chamber, a gas exhaust unit configured to partially exhaust gas from within the laser chamber, and a gas control unit configured to control the gas supply unit and the gas exhaust unit, where a replacement ratio of gas to be replaced from within the laser chamber increases as deterioration of the pair of electrodes progresses, the deterioration being represented by a deterioration parameter of the pair of electrodes.