To enable to adjust a location of a light focusing mirror in order to obtain uniform angle distribution characteristics in a short period of time in an extreme ultraviolet light source device.

Non-uniform angle distribution characteristics image data, and a movement direction and a movement amount of the light focusing mirror required to make the non-uniform angle distribution characteristics to uniform angle distribution characteristics, are recorded in a distribution database 10a in a controller 10. After obtaining the angle distribution image data from an angle distribution characteristics measurement apparatus 12, the angle distribution characteristics image data is compared with the images recorded in the distribution database 10a, and of the angle distribution characteristics image data, the image data are chosen that match most closely with the obtained current angle distribution characteristics. Then, data that are associated with the chosen image data and recorded, for knowing the movement direction and movement amount of the light focusing mirror 6 for achieving the uniform angle distribution characteristics, are read, and based on the data, the light focusing mirror 6 is moved by a light focusing mirror movement means 11.