Abstract: A folding step exerciser is provided with a main frame including a brace and two handlebars; a transmission device including two drive shafts on both sides of the brace respectively, a first rotating shaft below the drive shafts, a first wheel, a first belt linking the drive shafts and the first wheel, a second wheel, a connection rotating shaft between the drive shafts, a third wheel adjacent to the connection rotating shaft, a second belt linking the second wheel and the third wheel, and a flywheel connected to the connection rotating shaft; two pivotal length adjustable pedals on both sides of the main frame respectively; a pulley below the transmission device; a main belt linking the pulley, the drive shafts, and the pedals; a magnetic damping device for resistance adjustment; a sensor in close proximity to one pedal; and a numeric display between the handlebars.