A plug door opening-closing apparatus includes a lock mechanism, a drive mechanism, and a door support mechanism. The lock mechanism is directly or indirectly arranged on one of upper and lower portions of at least one door of a vehicle. The lock mechanism locks the door when completely closed so that the door does not open. The drive mechanism is coupled to the lock mechanism and drives the lock mechanism to switch the door from an unlocked state to a locked state. The door support mechanism is mechanically coupled to the lock mechanism and supports the door. When the completely closed door is switched from the unlocked state to the locked state, the door support mechanism is adapted to hold the door and hinder outward displacement, in a vehicle width direction, of the other portion of the door that is less the lock mechanism.