A laser apparatus includes an electric power supply system and a cooling water supply system. Both the electric terminals of the electric power supply system for connection with an external power cable and ports of the cooling water supply system for communicating with external pipes are placed in the forward part of the laser apparatus for facilitating its maintenance. A storage tank stores cooling water to be supplied to a laser oscillator. Both an ion exchanger and a filter are commonly housed in the tank to downsize the apparatus, to minimize the water leakage and to effectively purify the cooling water. Interchangeable flow control valves are provided for different electric power frequencies. According to the available power frequency an appropriate one of the valves is chosen and connected to internal piping to achieve the desired flow rate of the cooling water supplied to the laser oscillator.