PURPOSE: To manufacture a necessary number of core cylinders in a short time through the operation in a line, by joining the edge part of a batten plate which is bent by a direction change roll.

CONSTITUTION: A batten plate A is placed on a material table 11, and then horizontally slided so that the top edge of the strip plate A is bitten between pinch rolls 12 and 13. When a handle is turned, the strip plate A collides with a gudie 16a, and direction is changed, and the strip plate A is dropped downward, forming a curl on the strip plate A between the direction change roll 15 and the lower pinch roll 13. Then, the interval between the fixed drum piece of a joining board and a movable drum piece is reduced, and a bendable plate A1 having a curl is inserted between both the drum pieces and a material pressing part. Then, the interval of both the drum pieces is spread to obtain the necessary diameter. The bendable plate A1 having a curl is joined. Accordingly, a necessary number of strip-shaped coil core cylinders can be manufactured in a short time through the operation in a line.