A fitness device includes a body, a pedaling unit, a rotating unit, a seat unit, and at least one coupling unit. The coupling unit is pivotally mounted to the base and is coaxially aligned with the axle. The coupling unit is engaged with the rotating unit such that the rotating unit coaxially rotates with the coupling unit for driving the seat unit to convert between a first position in which the seat unit is located away from the base, and a second position in which the seat unit is located proximate to the base. A vertical distance and a horizontal distance between the seat unit and the pedaling unit are altered when converting between the first and second positions. By rotating the rotating unit, the horizontal and vertical distances between the seat and pedaling units are altered for allowing users to exercise in an upright posture or a recumbent posture.