Disclosed is a flexible roll forming device including: bases respectively disposed on opposite sides with respect to a process direction center line in a left/right direction, each having an opening formed in an upper side thereof connected to an inside thereof, and rails configured thereon on opposite sides of the opening in a lateral direction of the process; forward/backward moving cyclinder having a slide plate provided to be movable along the rails on the base; turning reducer rotatably provided to the slide plate; and upper and lower forming rolls provided on the turning cylinder for subjecting a material fed thereto to flexible roll forming by using the upper and lower forming rolls while varying positions in the lateral direction of processing with the forward/backward moving cylinder, and angles from a process direction with the turning reducer.