Holonomic omnidirectional mobile robot is useful with its high mobility in narrow or crowded place, and omnidirectional robot equipped with normal tires is desired for difference excess, vibration suppression and riding comfort. Caster-drive mechanism using normal tire has been developed to realize a holonomic omnidiredctional robot, however, there remains some problems. This paper presents effective systems to control the caster-drive wheels of omnidirectional mobile robot. Two kinds of Differential-Drive Steering System (DDSS) are proposed to improve the operation ratio of motors. One is using bevel pair gear and the other is using planetary gear to generate driving and steering torque effectively from two motors. Simulation results show the proposed system is effective for holonomic omnidirectional mobile robots.