In the manufacturing steps of rubber products such as tires, a strip-shaped belt member is used that is made of a plurality of steel cords disposed side by side at a predetermined cord angle and covered with rubber. This belt member is formed by cutting the member obtained by covering the steel cords disposed side by side with rubber, at a predetermined length and at a predetermined angle set in accordance with the cord angle, and bonding together a plurality of the cut members (See Japanese Unexamined Patent Application Publication No. 2009-226817A, for example). This strip-shaped belt member is wound around a molding drum and molded into a cylindrical shape. Further, a tread rubber forming a tire tread is molded into a cylindrical shape by winding strip-shaped unvulcanized rubber around the molding drum.
When the strip-shaped belt members and the strip-shaped unvulcanized rubber are wound around the molding drum in a meandering manner, a cylindrical member having strain in the width direction of the drum is molded. Further, in the cylindrical member molded by winding the plurality of strip-shaped members around the molding drum, also when the strip-shaped members are offset with respect to each other while being misaligned in the width direction by an amount greater than a set value, the strain in the width direction of the drum occurs in the cylindrical member. Manufacturing tires using the cylindrical member subject to this kind of strain makes it difficult to ensure consistent tire quality. Therefore, it is important to accurately assess a widthwise misalignment of the cylindrical member obtained by molding the strip-shaped member in the cylindrical shape.