To provide a braking device for a simplified vehicle automatically decelerating in a downhill slope, preventing backing of the simplified vehicle in an uphill slope, and capable of easily carrying out a change-over.

The braking device for the simplified vehicle has a fixed shaft 12 provided on a simplified vehicle body and rotatably supporting a hub 13, a gear mechanism 16 provided in an inner side of the hub 13, a turntable 17 connected with the gear mechanism 16 and having a rotational frequency different from the hub 13, a decelerating means 19 swingably provided on the turntable 17 and decelerating a wheel 58 by centrifugal force, a clutch mechanism 41 swingably provided on the fixed shaft 12 and provided with a change-over gear 56 capable of meshing or releasing meshing with one of an internal gear 29 or an external gear 16, and a change-over ring 47. The clutch mechanism 41 is provided with synchronizing members 74 and 75 energizing the change-over gear 56 toward the internal gear 29 or the gear mechanism 16 between the change-over ring 47 and the change-over gear 56, and it smoothly changes over a power transmitting state.