The medical dilator has a sustain portion and the auxiliary member. Auxiliary member has a insertable insertion portion into the opening, is inserted into the opening together with the insertion portion by being disposed in the insertion portion is disposed to intersect with respect to the insertion direction of the treatment instrument into the opening , and a support portion for supporting the treatment tool to be inserted into the opening.医療用拡張器は、維持部と補助部材とを有する。補助部材は、開口部に挿入可能な挿入部と、挿入部に配設されることによって挿入部と共に開口部に挿入され、開口部への処置具の挿入方向に対して交差して配設され、開口部に挿入される処置具を支持する支持部とを有する。
