Abstract: The present invention discloses an exercising apparatus designed to simulate the climbing of a staircase to achieve physical conditioning, including improved cardiopulmonary function and muscle-tone of the lower extremities. The present apparatus comprises a base-support structure on which is rotatably supported a stair mechanism defined by a rotatable member provided with two sets of step members. A plurality of left-step members and a plurality of right-step members are alternately offset from each other circumferentially to allow a step-climbing action by the operator. A gear drive is interconnected to a hydraulic system, the gear drive being operated by the rotation of the stair mechanism, which in turn operates the hydraulic system that includes a flow-control valve for regulating the rotation of the steps to suit the requirements of the individual operator.