The lift assistance system is aimed at daily life of persons who are handicapped with their legs. The system needs to clear the following requirements; riding easily, carrying easily. The innovative technology to clear them is extending mechanism with high extending capability. This paper introduces the new mechanism, roll-extending mechanism. This consists of bending legs which are divided into short blocks and chained each other with pin joints. The leg can bend and roll up to a single-side scroll from its initially straight shape. The one long, unbending and straight leg is derived from the two bending legs pairing with their back-to-back. Thus, the one long leg can shrink into short height with the roll-extending mechanism. The test production of the roll-extending mechanism has been manufactured.