A first roll (20) and a second roll (40) of a roll forming device are provided with a plurality of stacked cutting blades (22, 122) and retainers (21, 121). The retainers (21, 121) pass through the stacked cutting blades (22, 122) and receive a first rotating shaft (16) and a second rotating shaft (18). Projections (21a, 121a) are formed on end portions of the retainers (21, 121). When the cutting blades (22, 122) are stacked, the projections (21a, 121a) control positioning operation of the cutting blades (22, 122). With this constitution, when the cutting blades (22, 122) are joined in a stacked state to the retainers (21, 121), the cutting blades (22, 122) in the stacking direction is controlled with the retainers (21, 121).