A nasal mask comprising a pair of main bodies, which respectively form a containing space having an open end and a through-hole end; a connection which connects the edges of the opening ends of the main bodies; and a filtration device disposed inside the containing space of the main bodies. An alar projection is disposed at the upper brim of the opening end of the main bodies, which seals with the superior alar nasi of the nasal cavity. The main bodies forms a structure sealed with the nasal cavity. The main bodies of the nasal mask is made of soft elastic material and seals with the nasal cavity through the arrangement of an alar projection at the upper margin of the opening end of said main bodies that provides the wearer a sense of comfort.