Provided is a bending/stretching motion assist device that does not restrict the motion range of the upper body by being mounted on the lower body and efficiently assists the bending/stretching motion for raising and lowering the upper body. The bending/stretching motion assist device 1 is provided with: left and right thigh links 22； left and right lower leg links 23 swingably connected to the lower ends of the thigh links 22； a torso mounting member 2 which has an annular shape designed to be mounted around the torso and swingably supports the upper ends (25) of the left and right thigh links 22 on the lateral sides of the left and right hip joints； left and right lower leg mounting members 28 which are attached to the lower ends of the left and right lower leg links 23 and mounted around the corresponding lower legs； assist force generation devices (30, 40) for generating assist force in the direction of stretching between the lower leg links 23 and the thigh links 22 to assist the bending/stretching motion of the legs； and a hip support member 10 having a hip pad 12 which is disposed between parts (5) of the torso mounting member 2 near joint parts (25Xa) for the left and right thigh links 22, and is placed along the hip.L'invention concerne un dispositif d'assistance au mouvement de flexion/étirement qui ne limite pas la plage de mouvement du corps supérieur en étant monté sur le corps inférieur et assiste efficacement le mouvement de flexion/étirement pour soulever et abaisser le corps supérieur. Le dispositif d'assistance au mouvement de flexion/étirement (1) comprend : des liens de cuisse gauche et droite (22) ； des liens de jambe inférieure gauche et droite (23) reliées de façon à pouvoir effectuer une rotation convergente aux extrémités inférieures des liens de cuisse (22) ； un élément de montage de torse (2) qui présente une forme annulaire conçue pour être montée autour du torse et supporte en rotation convergente les extrémités supérieures (25) des lien
