The invention discloses a trismus trainer for a user's closed jaw, which comprises a first bracket, a second bracket and an adjusting member. A first bearing of the first bracket is coupled to a second bearing of the second bracket such that a first sheet of a first front end portion of the first bracket and a second sheet of a second front end portion of the second bracket are at a first angle, and the first angle can be determined by an adjustment member between the first operating portion of the first bracket and the second operating portion of the second bracket.本創作揭露一種開口訓練器作用於使用者的牙關，其包含一第一支架、一第二支架與一調整件。第一支架之第一軸承耦接第二支架之第二軸承，使得第一支架之第一前端部之第一薄片與第二支架之第二前端部之第二薄片夾設第一角度，並且利用在第一支架之第一操作部與第二支架之第二操作部之間的調整件，可以決定第一角度的角度。
