PURPOSE: To form a high strength cylinder easily by accomplishing the cylinder through coupling of a plurality of divisional pieces divided at least in the circumferential direction.

CONSTITUTION: A cylinder X either round or in polygon near round is formed by coupling a plurality of divisional pieces 13 divided at least in the circumferential direction. Each divisional piece 13 is formed by installing coupling flanges 22, 23 arranged up and down and on the left and right of a receptacle plate 21 with circular profile and by furnishing a reinforcing rib 24. These divisional pieces 13 are coupled together through bolts 26 and nuts 27 and the clearance holes 25 provided in the coupling flanges 22, 23. This permits easy forming of a cylinder X having a high strength.