An EUV light source apparatus capable of preventing the efficiency of generation of EUV light from decreasing due to deterioration of a window of an EUV light generation chamber. The EUV light source apparatus includes an EUV light generation chamber provided with a window, a driver laser which generates a laser beam, a concave lens which enlarges the laser beam, a convex lens which collimates the enlarged laser beam, a parabolic concave mirror which is arranged in the EUV light generation chamber and reflects the collimated laser beam to collect the laser beam to a target material, a parabolic concave mirror adjusting mechanism which adjusts position and angle of the parabolic concave mirror, an EUV light collector mirror which collects EUV light, and a purge gas supply unit which supplies a purge gas for protecting the window and the parabolic concave mirror.