An folding exercising machine includes an upright with a bottom frame for positioning on a floor, two handlebars pivotally coupled to the upright at two sides, two pedal frames respectively pivoted to the bottom sides of the handlebars, each pedal frame having a bottom pin, a wheel module pivoted to the bottom frame of the upright and alternatively set between an operative position and a non-operative position, a lock screw provided at the bottom frame of the upright for locking the wheel module in the operative position, two first sockets respectively provided at two pedal cranks of a wheel of the wheel module for receiving the bottom pins of the pedal frames to hold the wheel module in the operative position, two second sockets provided at a transverse bar at the rear side of the wheel module for receiving the bottom pins of the pedal frames to hold the wheel module in the non-operative position, and a retaining member provided at the upright for locking the wheel module in the non-operative position.