An extreme ultraviolet light source apparatus includes a disc-shaped cathode rotating about an axis, a disc-shaped anode rotating about an axis, an energy beam irradiation device irradiating a plasma raw material on the cathode with an energy beam to vaporize the plasma raw material, a power supply for causing a discharge between the cathode and the anode for generating a plasma in the gap between the cathode and the anode to emit extreme ultraviolet light, and an irradiation position adjusting mechanism for adjusting a position at which the cathode is irradiated with the energy beam. The cathode, the anode, and the irradiation position adjusting mechanism are accommodated in a housing. A photography device is disposed outside the housing and is configured to photograph a visible-light image of a vicinity of the cathode and the anode, the vicinity including visible light emitted from the plasma.