A light source device capable of extending the life of a collector mirror and reducing running cost by protecting the collector mirror from debris that is considered harmful to a mirror coating while securing the collection solid angle and collection rate of EUV light. The light source device includes a target supply unit for supplying a material to become the target; a laser unit for generating plasma by applying a laser beam to the target; a collection optical system for collecting the extreme ultra violet light radiating from the plasma and emitting the extreme ultra violet light; and magnetic field generating unit for generating a magnetic field within the collection optical system when supplied with current so as to trap charged particles radiating from the plasma.