a mask body ( 4 ) including a mask shell (41), and a mask cushion (42) connected to a rear side of the mask shell (41) a front cover (32) disposed in front of and hinged to the mask shell (41), and having a support arm (320) extending upwardly a forehead support unit (3) having a forehead frame (31) connected to a top end of the support arm (320), and a forehead pad (33) connected to a rear side of the forehead frame (31) and an adjustment unit (6) connected to at least one of the mask shell (41) and the front cover (32) , and operable to produce relative movements of the mask shell (41) and the front cover (32) so that the mask body (4) can abut against the user"s nose with an appropriate abutment pressure. Fig. 2
