A cart braking device includes a swivel unit, a shaft unit and a braking unit which has a central shaft, an orientation member, a braking member and a base. The central shaft is coupled with the orientation member and has an elastic piece for moving the central shaft upward. A bottom of the orientation member has an orientation gear and a top of the braking member has a fixation gear corresponding to the orientation gear. The braking member is disposed in the base and includes two braking pads. An elastic member is disposed between the base and the braking member, and can move the braking member away from the base. When the braking pads are pressed against the wheel, the cart braking device stops the rotation of the wheel. When the orientation gear is engaged with the fixation gear, the cart braking device prevents the wheel from changing direction.