A flexible die is used in an embossing apparatus in which a pair of flexible bases (2a, 2b) are respectively wrapped around a pair of cylindrical rollers disposed opposing each other, and a sheet to be processed (S) is passed through between the pair of rollers, thereby performing embossing. The pair of flexible bases (2a, 2b) are constituted by a female flexible base (2a) and a male flexible base (2b) that are mated with each other, a line-shaped convex portion (3a) corresponding to the contour of an embossing processing pattern is formed in the female flexible base (2a), and the convex portion (3b) is formed in the male flexible base (2b), the convex portion (3b) being fitted within the area encompassed within the line-shaped convex portion (3a) of the female flexible base while leaving an interval from the inner circumferential surface of the line-shaped convex portion (3a). A concave portion (30) is formed in the convex portion (3b).