An EUV (extreme ultra violet) light source device in which a degree of vacuum or cleanness in a plasma generation chamber is improved while the construction is simplified. The device includes a first chamber; a second chamber connected to the first chamber through an opening portion; a target supplier that supplies a target material into the first chamber; a droplet generating unit that generates droplets of the target material of molten metal repetitively dropping based on the target material supplied by the target supplier; a blocking unit that prevents the droplets of the target material generated by the droplet generating unit from passing through the opening portion; control unit that controls the blocking unit to operate at predetermined timing; a laser light source; and an optical system that leads a laser beam to the droplets of the target material introduced into the second chamber.