The present invention relates to a treadmill exercise machine (M) of the type employable for physical training or rehabilitation exercises, having a base structure (1) able to support a belt (2) whereon act related motor means (3) able to drive the belt itself along a closed path, in such a way as to define, in correspondence with at least an upper portion of the path, an area (Z) destined for the execution of an exercise, i.e. in such a way as to provide a user with an area (Z) in which the belt (2) is movable according to a speed (V) parallel to the development of two cross elemetns (4) of the structure (1), and a direction (A) determined according to the exercise to be executed; on the base structure (1) is positioned, inferiorly to the area (Z) destined to the execution of an exercise, a platform (5) defining a bearing for the user when the latter is on the area (Z) and movable or disengageable means (6) are present, destined to allow the replacement of the belt (2) with another belt having different reaction and/or yielding characteristics.