PROBLEM TO BE SOLVED: To provide a mouth opening trainer capable of performing the rotational motions and the forward sliding motions of a mandible joint continuously smoothly so that the motions of a lower jar may be guided to trace the loci of the actual opening motions of an actual lower jaw.SOLUTION: A mouth opening trainer 1 comprises: an upper member 2 gripped on the side of a base end 11 and capable of engaging with the side of a leading end 12 with the upper jar of the user； a lower member 3 capable of engaging on the side of the leading end 12 with the lower jaw of the user and slidably contacting partially with the upper member 2； and a connecting portion 5 connecting the upper member 2 and the lower member 3 slidably and openably. As the side of the leading end 12 of the upper member 2 and the side of the leading end 12 of the lower member 3 are opened, the lower member 3 moves toward the leading end 12.【課題】顎関節の回転運動と前方滑走運動を連続してスムーズに行うことができ、これにより、実際の下顎の開口運動の軌跡をトレースするように下顎の運動を誘導させることのできる開口訓練器を提供すること。【解決手段】開口訓練器１は、基端１１側が把持されるとともに先端１２側が使用者の上顎に係合可能な上部材２と、先端１２側が使用者の下顎に係合可能であり、一部が上部材２とスライド可能に接している下部材３と、上部材２と下部材３とをスライド可能かつ開閉可能に連結する連結部５と、を備え、上部材２の先端１２側と下部材３の先端１２側とを開くに従って、下部材３が先端１２側に移動する。【選択図】図１
