A treadmill includes a base, two axle units, two pedal units and a coordinating unit. The base includes a post formed thereon. Each of the axle units includes an axle extended downwards from the post. Each of the pedal units includes a pedal pivotally connected to the axle of a related one of the axle units. The coordinating unit is used to connect the pedals to each other so that one of the pedals is moved upwards and outwards while the other pedal is moved downwards and inwards.