A lower extremity support tool (10) includes: a right and a left foot parts (11), each comprises a curved face on a back face thereof facing a ground surface, the right and the left foot parts each having one foot of both of feet of a user individually placed thereon on a front face thereof a right and a left leg parts (13), the right leg part being connected to the right foot part, the left leg part being connected to the left foot part, the right and the left leg parts each extending along an area of one of both legs of the user a lower back part (14) disposed in an area of a lower back of the user, the lower back part rotatably supporting individually each of the right and the left leg parts, the lower back part including a right and a left motors (15) each causing one of the right and the left leg parts to normally rotate or reversely rotate and a control part (16) that controls the normal rotation and the reverse rotation of each of the the right and the left motors (15) in the lower back part (14), while the curved face of the back face of one of the foot parts faces the ground surface to grab the ground surface, the one of the foot parts being connected to one of the leg parts, such that the motor causes the other of the leg parts to normally rotate when the other of the leg parts kicks the ground surface back ward, or the motor causes the other of the leg parts to reversely rotate when the other leg part is swung forward, wherein walking by a passive walk mechanism is realized, the curved faces of the back faces of the right and the left foot parts alternately facing the ground surface to grab the ground surface alternately in the passive walk mechanism.
