An active caster is developed as a distributed actuation module which can endow objects with mobility on the planar workspace. Kinematics of a mobile robot with the proposed double-wheel-type active caster is investigated in this paper. A closed form kinematics of omni-directional mobile robot which consists of multiple double-wheel-type active casters is studied. Besides, kinematic characteristic is analyzed by using kinematic isotropic index and force transmission ratio. As a result, optimal condition for the robot employing the proposed double-wheel-type active caster is also proposed.