A load port including: a base as part of a wall partitioning a transportation space from an external space; an opening provided to the base; a door configured to open and close the opening and securing a lid to, and releasing a lid from, a container containing contents; and a first seal member for sealing the space between the base and the container. At least some of the container-side end surface of the door is located nearer to the transportation space than the container-side end part of the first seal member. The load port can keep a surrounding space clean when a FOUP is connected to a casing.