To avoid escaping of a wheel(s) from a rail(s) when a boggie loading a stirring mechanism is changed in its direction on an endless route in a sewage treatment process and also to stabilize the boggie when it enters a direction change position on the endless route and when it comes out of the direction change position.

This device has a center rail 11 on which a pair of inner wheels of a boggie 2 run, a pair of side rails 12, 12 on which an outer wheel thereof run, a circular-arc-shaped turn rail 13 connecting ends of the side rails 12, 12 mutually. The center rail 11 is divided into a fixed rail part 15 and a movable rail part 16. The longitudinal center of the movable rail part 16 is supported so as to be rotatable at the center of the circular arc of the turn rail 11. The movable rail part 16 has a positioning mechanism to the fixed rail part 15 and a level matching mechanism.