PURPOSE: To prevent a cooling medium from leaking into a bearing part, even if a sealing member is deteriorated, by making a structure in which a ring- shaped blocking member with a feeding and discharging port of the cooling medium is brought into contact with a roll body through a sealing member thereby blocking the opening of a grooved recessed part in the roll body.

CONSTITUTION: A roll assembly A is constituted of a sleeve 6, sleeve cap 7, roller bearing 8 supported with these parts, roll piece 1 supported by a shaft 5, holder 9 and ring shaped blocking member 2. The opening of the grooved recessed part 1a formed in the roll piece 1 is blocked by the ring-shaped blocking member 2 through a sealing member 4-1 to form a passage P for a cooling medium. The ring-shaped blocking member 2 is provided with a feeding port of the cooling medium, discharging port and partition 2a. Since the partition 2a blocks the passage P, the cooling medium enters from the feeding port to the passage P, and goes out from the discharging port, cooling the roll piece 1. The bearing 8 is arranged inside the inner diameter of the roll piece 1 in separation from the sealing part 4-1; and therefore, the cooling medium does not leak.