A mask comprising: a mask main body that covers a target part on a wearer's face; and a pair of right and left ear hooks (2, 3) for locking the mask main body to the wearer's ears, wherein the mask main body comprises: a sheet comprising sheet materials stacked in three or more layers; a plurality of pleats unfoldable in an up-down direction; and a mouth reinforcement member for ensuring a first interval between a wearer's mouth and the mask main body, the plurality of pleats comprise an upper pleat which is a fold projecting upward and formed above a center of a front surface of the mask main body in the up-down direction and a lower pleat which is a fold projecting downward and formed below the center of the front surface of the mask main body in the up-down direction, the mouth reinforcement member is provided below a center of the mask main body in the up-down direction, the mask being characterized in that the mouth reinforcement member is attached to the sheet by welding at least two of the sheet materials to form a bag-shaped space substantially coinciding in shape with the mouth reinforcement member and placing the mouth reinforcement member in the space without welding a sheet material at a foremost layer among the sheet materials. a mask main body that covers a target part on a wearer's face; and a pair of right and left ear hooks (2, 3) for locking the mask main body to the wearer's ears, wherein the mask main body comprises: a sheet comprising sheet materials stacked in three or more layers; a plurality of pleats unfoldable in an up-down direction; and a mouth reinforcement member for ensuring a first interval between a wearer's mouth and the mask main body, the plurality of pleats comprise an upper pleat which is a fold projecting upward and formed above a center of a front surface of the mask main body in the up-down direction and a lower pleat which is a fold projecting downward and formed below the center of the front surface of the mask main body in the up-down direction, the mouth reinforcement member is provided below a center of the mask main body in the up-down direction, the mask being characterized in that the mouth reinforcement member is attached to the sheet by welding at least two of the sheet materials to form a bag-shaped space substantially coinciding in shape with the mouth reinforcement member and placing the mouth reinforcement member in the space without welding a sheet material at a foremost layer among the sheet materials. a sheet comprising sheet materials stacked in three or more layers; a plurality of pleats unfoldable in an up-down direction; and a mouth reinforcement member for ensuring a first interval between a wearer's mouth and the mask main body, the plurality of pleats comprise an upper pleat which is a fold projecting upward and formed above a center of a front surface of the mask main body in the up-down direction and a lower pleat which is a fold projecting downward and formed below the center of the front surface of the mask main body in the up-down direction, a plurality of pleats unfoldable in an up-down direction; and a mouth reinforcement member for ensuring a first interval between a wearer's mouth and the mask main body, the plurality of pleats comprise an upper pleat which is a fold projecting upward and formed above a center of a front surface of the mask main body in the up-down direction and a lower pleat which is a fold projecting downward and formed below the center of the front surface of the mask main body in the up-down direction, the mouth reinforcement member is provided below a center of the mask main body in the up-down direction, the mask being characterized in that the mouth reinforcement member is attached to the sheet by welding at least two of the sheet materials to form a bag-shaped space substantially coinciding in shape with the mouth reinforcement member and placing the mouth reinforcement member in the space without welding a sheet material at a foremost layer among the sheet materials.