An EUV light source device for protecting a collection mirror from debris that is considered harmful to a mirror coating. The EUV light source device includes: a chamber in which extreme ultra violet light is generated; a target injection unit and a target injection nozzle that supply the chamber with a material to become the target; a laser light source that applies a laser beam to the target so as to generate plasma; a collection mirror that collects the extreme ultra violet light emitted from the plasma; an X-ray source that ionizes neutral particles included in particles emitted from the plasma into charged particles; and plural magnets that generate a magnetic field within the chamber so as to trap at least the charged particles ionized by the X-ray source.