To enable connection/disconnection of rail devices to/from each other using a simple structure, in a movable rail device capable of connecting/disconnecting to/from a traveling rail device on which a carrier travels.

A maintenance carriage 15 is the movable rail device capable of connecting disconnecting to/from a circulating track 3 on which the carrier 5 travels. The maintenance carriage 15 is provided with a pin 33. The maintenance carriage 15 includes moving rails 25 on which the carrier 5 can travel/stop, and wheels 23 allowing the carriage to move on the moving rails 25. When the moving rails 25 are connected to the circulating track 3, the pin 33 can move to a first position where the pin 33 holds the maintenance carriage 15 at a predetermined position. When the moving rails 25 are disconnected from the circulating track 3 while placing the carrier 5 thereon, the pin 33 can move to a second position where the pin 33 prevents the carrier 5 from dropping out from the moving rails 25.