To provide a sealing structure of a cap in a transportation vessel, particularly, a vessel where sealing ability is required, such as a vessel for treating medical wastes, which can further ensure the sealing ability of an opening.

In the transportation vessel where a round R1 is formed on a flange 6 of a vessel body 2 so as to allow a cap body 8 to easily fit to the vessel body 2, an inner shoulder part S1 is bulged to the flange 6 side so that the distance between the shoulder part S1 of a recessed locking part 10 and a ceiling face of the flange 6 becomes almost uniform.