PURPOSE: To improve the roundness of thin wall tube body by providing the cooling mechanism for circulating the coolant in the inside of the bending roll.

CONSTITUTION: The coolant passing route 12 passing through the central part of the roll body 11 is drilled on the bending roll 10 of the both ends supported type. On the case of the floating roll, the simple tube like roll is used. The water and the cool wind, etc., are used as the coolant, and the roll body 11 is kept under the set temperature by changing the fluid. In such a way, when the metallic strip is bent in plastic while cooling the roll body 11 with the coolant, the elavation of temperature of the roll body 11 heated with working is restricted. So, the initial shape of the roll is kept, the residual stress of the strip is made uniform to the lateral direction because it is worked on the same condition.