A collision force suppression system for a human friendly robot, which consists of two arms, a trunk, a waist, an omnidirectional mobile base, is proposed. In this paper, the proposed passive collision force suppression system is realized by the collision force suppression mechanisms and the reaction system. When the collision occurs between the robot and an object, the joints of the arm and the waist are disconnected by the collision force suppression mechanism depending on the magnitude of collision forces. The reaction system is based on the strength and existence time of the collision force, and the joints are disconnected by the order of arm and waist, and the finally the mobile base will move if the reactions are not enough to decrease the passive force. The effectiveness of the proposed system is proven by experiments.