To provide a structure for reinforcing an embankment which can prevent a boundary between a terminal end of a countermeasure section with sheet piles and a section without a countermeasure from becoming more vulnerable to a seepage flow than an embankment before the reinforcement.

The structure prevents the seepage destruction of the embankment 1 by providing a cut-off wall formed of an underground steel-wall body 2 along the continuous direction of the embankment 1 in the embankment 1 serving as a dike of a river etc. In the structure, the countermeasure section (b) with the sheet piles which is provided with the underground steel-wall body 2, and the section (c) without the countermeasure which is not provided with the underground steel-wall body 2 yet exist in such a manner that the end of the underground steel-wall body 2 already provided but still being under reinforcement construction serves as the boundary. The vertical cut-off wall 6 which is formed of the underground steel-wall body extending toward the outside of the dike in a direction almost perpendicular to the end of the underground steel-wall body 2 is provided at the end of the underground steel-wall body 2. The depth of the embedment of the vertical cut-off wall 6 is set larger than that of the embedment of the underground steel-wall body 2 along the length direction of the embankment 1.