a neck hanging part; and

a mask body connected with the neck hanging part, a concave space being formed on an inner side of the mask body, a plurality of air vents communicating with the concave space being formed in a lower half of an outer side of the mask body, and a plurality of inclined retaining walls being located in the concave space and respectively connected to a top edge of each of the plurality of air vents, and the plurality of inclined retaining walls being capable of preventing the concave space from being seen when viewed directly through the plurality of air vents of the mask body.