An apparatus and method accurately measures an amount of overlap in joining together the end portions of a sheet-shaped member constituting a tire. The overlap amount of the sheet-shaped member front and rear ends is measured when the sheet-shaped member having been molded into a predetermined length with molding marks extending on the surface in width direction is wound around the periphery of a molding drum from the front end. In doing so, a detector detects a first molding mark formed on the sheet-shaped member on the rear end side and a second molding mark formed on the sheet-shaped member on the front end side by capturing images of an entire area including the overlap from above by an image capturing device. A calculator calculates the amount of overlap by measuring the distance between the first and second molding marks on the sheet-shaped member from the frames of captured images.