PROBLEM TO BE SOLVED: To provide a vial adaptor capable of locking a plurality of vials different in an outside diameter of a vial top surface and capable of sufficiently securing a locking member.SOLUTION: A vial adaptor 1 comprises a locking member 6 that is brought into contact with an outer wall of a vial with a plug body and that locks the vial. The locking member can move in a radial direction of a top surface depending on an outside diameter of the approximately circular top surface of the vial. Thus, the vial adaptor 1 can lock the plurality of vials different in the outside diameter.
