NOVELTY - The treadmill has a tread belt device (2) pivotally secured to a main frame (1). A set of rollers are mounted on columns of the main frame. A handle (14) of the main frame is grasped by a user to push or pull the treadmill ergonomically, such that columns are slid along a corner of a pool wall and wheels (13) are rolled on the pool wall. A hand rail device (3) has hand rails (31) and supporting bars (32) that are raised and erected, respectively. The belt device is laid on a pool bottom, and locking bolts (34) are fastened to assemble the treadmill.    USE - Used for underwater exercising or hydrotherapy, by user e.g. hydrotherapeutic patient. Can also be used on a land, in gym and in a pool.    ADVANTAGE - The user grasps the handle of the main frame to push or pull tread mill ergonomically, such that the columns are slid along the corner of the pool wall and wheels are rolled on the pool wall, thus allowing the treadmill to be safely, smoothly and conveniently launched into a pool. The user grasps the handle of the main frame to push or pull the treadmill ergonomically, so that the treadmill is easily and conveniently moved by pushing or pulling the treadmill, thus allowing the treadmill to be folded to greatly minimize the volume, so that the treadmill is easily carried or handled by a car, and is used by a hydrotherapeutist patient. The belt device is laid on the pool bottom, the hand rails are raised, the supporting bars are erected and the locking bolts are fastened to stably assemble the treadmill, thus allowing the treadmill to be quickly folded for treading use. The rollers are mounted on the columns, thus preventing pool wall from scratching or damage. The treadmill can be folded for convenient handling, moving, launching in a pool or landing on the ground floor from the pool. The treadmill is quickly and conveniently folded or unfolded and is either used on a land or in a pool, thus providing an amphibious treadmill.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a treadmill.    Main frame (1)    Tread belt device (2)    Hand rail device (3)    Belt pivot (10)    Wheels (13)    Handle (14)    Rail pivot (15)    Impellers (23)    Hand rails (31)    Supporting bars (32)    Locking bolts (34)