Reinforcing sheet for steel plate

A steel plate reinforcing sheet that can reduce distortions of the steel plate without reducing its reinforcing property and can also prevent abrupt deformations at end portions thereof with respect to a direction extending along a curving direction of a curved steel plate. The steel plate reinforcing sheet 1 comprising a restricting layer 2 and a reinforcing layer 3, wherein slits 4 are formed in both end portions of the restricting layer 2 to extend over an entire length of the restricting layer 2 with respect to a direction substantially orthogonal to a direction in which the both end portions confront each other and also arranged so that a length defined between the slits 4 can be 40% or more of a total length of the steel plate reinforcing sheet 1 with respect to a direction parallel to the length between the slits 4. Then, the steel plate reinforcing sheet 1 is adhesively bonded to the curved steel plate 5 so that the slits 4 extend along a direction substantially orthogonal to the curving direction of the curved steel plate 5 and, then, is foamed and cured.