PURPOSE: To simplify the structure, and to minimize chipping work by forming a T-shaped groove split by intermediate webs which are opposite to each other in section, and perpendicular to a slide plate on a longitudinal rail in a frame comprising a pair of arranged longitudinal rails, the slide plate, and a bearing bed.

CONSTITUTION: Two longitudinal rails 16 having two T-shaped grooves 22, 23 separated from each other by one center web 49 are connected parallel to each other with intervals through a transverse beam 15. An upper covered part comprises a belt wall 13, a flange extending in the longitudinal direction is formed in a lower area, and a T-shaped groove 24 opposite to right and left flanges 18, 18 is formed. A slide plate 6, bearing beds 35, 36 for a drive roller 28, and a bearing bed 34 for a backing roller 27 are arranged, and a conveyor belt 40 is stretched. These required members are arranged continuously at an arbitrary position making use of two grooves opposite to each other. The chipping work is thus minimized to simplify the constitution.