Abstract: The present invention is related to a rehabilitation apparatus to alleviate the stiffness for patients suffering from lower limb paralysis caused by acute cerebral vascular impairment or vertebra impairment. The essential mechanisms of the rehabilitation apparatus include a transversely movable slider mechanism which makes use of a transverse slider capable of moving in a predetermined direction and for a predetermined distance to provide the thigh with reciprocal motion of inward retraction and outward expansion by means of a spherical joint which drives the rotation of a longitudinal slide rail, the outward expansion or inward retraction having an angular range between 0.degree.-35.degree.