A filter structure includes a blower having a gas suction opening, the blower compressing gas taken from the gas suction opening and supplying the compressed gas to respiratory organs of a patient； a housing that contains the blower and has air passage openings connected to the gas suction opening； a bag at least part of which is made of a nonwoven paper as a filter material, for covering the housing； and a chamber forming member disposed between the housing and the bag, for forming a chamber CAM between each air passage opening and the nonwoven paper. Thus, effort for maintenance of a filter is reduced.
