PURPOSE: To use an existing roller table as it is by mounting a joining device on a traveling truck, providing an inlet tilting table and outlet tilting table so that a belt-like metal sheet is returned from the roller table to the roller table through the joining device.

CONSTITUTION: When a joining part in the state that the rear end of the preceding belt-like metal sheet 41 and the tip of the succeeding belt-like metal sheet are approximately brought into contact comes into the joining device 31 by traveling on the rollers of the inlet tilting table 32 from the roller table 45, the joining part is clamped and joined with the traveling truck 30 whose speed is equalized to the speed of the belt-like metal sheet while running parallel each other. The preceding belt-like metal sheet reaches down to the roller table 45 from on the rollers of the outlet tilting table 33. When joining is completed, the traveling truck 30 is stopped, but the belt-like metal sheet 41 is traveled on the rollers of the inlet tilting table 32, joining device 31 and outlet tilting table 33. In this state, the traveling truck is returned to the initial position. In this way, the level difference between the roller table and the clamping part of the joining device is linked and the belt-like metal sheet 41 is joined.