A roll stamper for forming a substrate sheet for information recording mediums has a flexible stamper member having a pattern corresponding to a preformat for an information recording medium; a first fixing member and a second fixing member respectively joined to both ends of the stamper member in an integral form; and a pair of fit grooves capable of fittingly receiving the fixing members, formed in the periphery of a specular roll substrate in parallel to the axial direction of the specular roll substrate. The fixing members are so fitted to the fit grooves that the stamper member is fixed along the periphery of the specular roll substrate between the fit grooves.The first fixing member has a first member showing a coefficient of linear expansion substantially equal to the coefficient of linear expansion of the stamper member and a second member having a larger coefficient of linear expansion than the coefficient of linear expansion of the first member. The first member is joined to the stamper member and the second member is positioned inside the first member with respect to the second fixing member. The roll stamper is so set up as to satisfy the relationship of expression (1):.DELTA.L.sub.1 -.DELTA.L.sub.2