Abstract: In an excimer laser apparatus comprising a laser chamber 1 filled with a laser gas, a discharge excitation portion 2 provided in the laser chamber 1, a rotary shaft 3 to which a gas circulating fan 4 for circulating the laser gas is fixed, a shield partition wall 61 for forming a sealed space to enclose the rotary shaft 3, a magnetic bearing of a control type including a rotor portion 32 provided on the rotary shaft 3 side and a stator portion 6 provided outside the shield partition wall 61 and serving to pivotally support the rotary shaft 3 in non-contact, a driving motor 13 provided outside the laser chamber 1, magnetic coupling portions 33, 11 and 121 for transmitting driving force of the driving motor 13 to the rotary shaft 3 through the shield partition wall 61 in non-contact, and rotary shaft sensors 8 and 9 for detecting a position of the rotor portion 32 with respect to the stator portion 6.