[PROBLEMS] An impact absorption body for a vehicle can have desired impact absorption performance, exhibits excellent impact absorption performance particularly immediately after an impact is applied to the body, and can maintain high impact absorption performance. [MEANS FOR SOLVING PROBLEMS] The impact absorption body (1) for a vehicle is installed within a vehicle forming member and absorbs impact energy in a collision. The impact absorption body (1) has a first wall (4) placed on the side that receives an impact, a second wall (5) facing the first wall (4) with a hollow section (2) between them, and one or more impact absorption ribs (9) constructed from deep groove sections (15) and shallow groove sections (16). The deep groove sections (15) are formed by depressing the first wall (4) and second wall (5) into groove shapes and integrally joining the top surfaces, which function as fusion bonding surfaces, of the depressions. The shallow groove sections (16) are formed by causing the top surfaces of the depressions to face each other with gaps between them.