There is provided a light source system that may include a free electron laser apparatus, a light concentrating mirror, and a delaying optical system. The free electron laser apparatus may include an undulator, and may be configured to output a pulsed laser light beam toward an exposure apparatus. The light concentrating mirror may be configured to concentrate the pulsed laser light beam to enter the exposure apparatus. The delaying optical system may be provided in an optical path between the undulator and the light concentrating mirror, and may be configured to delay the pulsed laser light beam to allow an amount of delay of the pulsed laser light beam to be varied depending on a position in a beam cross-section of the pulsed laser light beam.
