PURPOSE: To facilitate the car maneuvering operation with a track device, with which a vehicle reciprocates between the starting point of an aux. track and the working point on a main track, and enhance the effectiveness in works by forming a circumferential guide groove in the peripheral surface of a disc wheel which runs on the rail of the aux. track.

CONSTITUTION: A guide plate 6 is provided projectingly at each edge of the peripheral surface of an outer disc wheel 231 of a dolly 23 for transportation of a retaining furnace, and thus a guide groove 61 is formed. An aux. track outer rail 21 and a main track in continuity thereto are fitted in this guide groove 61. An inner disc wheel 232 is supported in the condition simply placed upon an inner rail 22. Thereby the dolly runs on the outer rail 21 while guided by the circumferential guide groove 61.