A caster includes a caster unit and at least one braking unit. The caster unit includes a receptacle, a wheel shaft disposed through the receptacle, a wheel assembly sleeved on the wheel shaft and rotatable relative to the receptacle, and a spring assembly which acts on the receptacle and the wheel shaft. The receptacle is movable relative to the wheel assembly in a vertical direction. The braking unit includes a surrounding teeth structure formed on the wheel assembly and having a hardness ranging from 65 to 75 on a Shore D scale, and a braking piece mounted on the receptacle. The braking piece includes a braking surface in form of a curve surface having a hardness ranging from 40 to 46 on the Shore D scale to be engaged with the surrounding teeth structure to retard rotation of the wheel assembly.