A respiratory assistance device 10 includes: a mask 13having an expiratory hole 13a an expiratory valve 15 providedin the mask 13, for opening and closing the expiratory hole13a and a control unit 17 for performing overall control onthe entire device. The mask 13 and the expiratory valve 15together form an opening and closing device. The expiratoryvalve 15 is deformable by deformation of a piezo element 15a.The expiratory valve 15 is disposed on an inner surface 13f sothat a deformation direction thereof, i.e., a thicknessdirection thereof, extends along the inner surface 13f of themask 13 and a side surface 15m slides along the inner surface13f by the deformation thereof.
