The ventilation device according to the invention comprises a mouth ventilation mask (10) which, during use, does not cover the nose of a patient wearing the device and which comprises an elongated body (11) for channelling the patients respiratory exchanges, said body being provided with a peripheral skirt (15) covering the patients mouth, and a harness (20) for fastening the mask on the patient, which comprises both a strap (21, 22) suitable for surrounding the patients head, and a mechanical connecting part (30) between the mask and the strap(s), said connecting part delimiting a hole (46) for receiving the body of the mask such that, when the device is in a usage configuration, in which the body of the mask is received in the body of the connecting part and the strap(s) are tightened around the patients head, the connecting part keeps the mask in place on the patients mouth, while pressing against the skirt of the mask. In order to improve patient comfort, the invention provides that, in the usage configuration, the skirt of the mask and the connecting part of the harness cooperate with each other by sliding bearing.Ce dispositif de ventilation comporte un masque buccal de ventilation (10), qui, en service, ne couvre pas le nez dun patient portant le dispositif et qui comprend un corps allongé (11) de canalisation des échanges respiratoires du patient, ce corps étant pourvu dune collerette périphérique (15) de recouvrement de la bouche du patient, et un harnais (20) de fixation du masque sur le patient, qui comprend, à la fois, au moins une sangle (21, 22) adaptée pour entourer la tête du patient, et une pièce (30) de liaison mécanique entre le masque et la ou les sangles, cette pièce de liaison délimitant un trou (46) de réception du corps du masque de manière que, lorsque le dispositif est dans une configuration de service, dans laquelle le corps du masque est reçu dans le corps de la pièce de liaison et la ou les sangles sont serrées autour de la tête du pati
