A locking system for a tricycle, including a braking mechanism, a rolling restraint mechanism, a driving mechanism which drives the braking mechanism and the rolling restraint mechanism, a control mechanism for applying control signals, and a detecting mechanism for applying a speed signal to the driving mechanism when a vehicle speed is lower than a predetermined value. The driving mechanism selectively or simultaneously drives the braking and restraint mechanisms in response to the control signal, and also drives the restraint mechanism upon receiving the speed signal. With such arrangement, maximum freedom is afforded the driver in assuming a desired posture, even when the tricycle is travelling under low inertia.