Provided is a mouthpiece that does not come off easily even when a user suddenly moves, and that can alleviate snoring, apnea and symptoms of obstructive respiratory disorders. The mouthpiece has an upper piece (2) that fits to a row of teeth of an upper jaw (J1), a lower piece (3) that fits to a row of teeth of a lower jaw (J2), and a connecting member (4) that connects the upper and lower piece (2 and 3) so that the pieces are in a preset target position and so that the upper piece (2) and the lower piece (3) are relatively displaced while generating elastic force for returning to the target position by elastically deforming the connecting member according to an external force applied to at least one of the upper piece (2) and the lower piece (3).
