To provide a lock structure of an expandable gate, facilitating operation of a drop bar and having high degree of freedom in design.

This lock structure of an expandable gate includes: a lock member provided on the movable side end part of the expandable gate; a lock receiver engaged with the lock member; and an operating part for operating the lock member, wherein the lock member and the lock receiver are engaged with each other to accomplish locking. In the lock structure, the drop bar mounted on the expandable gate interlocks with the operating part, so that when the lock member and the lock receiver are engaged with each other to perform locking, the drop bar is moved to the lower side.