PURPOSE: To deal with the production of many kinds in small quantities by changing roll size quickly at a set of roll forming stands and reducing the dead time of a line.

CONSTITUTION: A forming line 1 composed of many cold roll forming stands 5 through which a panel material 3 is passed to form a prescribed shape is equipped on a truck 2 which can be displaced in the direction crossed with the line 1. The roll forming line 1 is composed of a 1st forming line 1A consisting of many stands 5A arranged at equal pitches (p) and a 2nd forming line 1B consisting of many stands 5B, 5B arranged in parallel with the 1st line 1A and shifted by half a pitch from that of the line 1A. When A transmission gear and an idle gear which are arranged corresponding to stands 5 are put in the engaging state, all rolls 7 of the selected forming line are rotated by a single change-over gear and a driving means 6 at the same time in the same direction. In the forming line which is not selected, the roll size is changed when the other line is under working.