The subject innovation is the front plate provided with a roller wheel at the bottom surface; The back plate having the roller wheels on the bottom surface; Leaf spring members for connecting the front plate and the back plate; And made including a fastening member, each fixed to the board at both ends of the front plate and the rear plate of the spring member, and wherein the leaf spring members are mutually corresponding plurality of leaf spring having a fitting hole, respectively, which in both ends have been side-by-side nested is, the fastening members to the both ends of the "c" shape to be fitted in the plate spring member, and then the bottom surface of the front plate end, and are respectively formed integrally with the bottom front end of the rear plate, in the "c" shape both sides of the said plate is fitted ball and the ball formed fastening to each communication of the spring member and the fitting piece inserted through the fastening holes and the fitting holes, the fitting piece is formed of a ball screw in the vertical direction in both end portions corresponding to the fastening holes the "c" shape of the side walls at the top is formed with the screw hole in which the threaded hole in communication with the top-bottom direction of the fitting hole by screwing through the screw hole and the screw groove to be thereby fixed to the fitting piece to the fastening member springs as resilient driving board, through such a configuration improves the resilience and at the same time easy to straightness and the weight distribution and the change direction can be improved driving ability.