Robust control is used for a system with uncertainties and disturbances. Above all, the H∞ loop shaping method is known as the method achieving good control performance. However, this method takes much time to build the mathematical model of an actual plant and its uncertainty. In this paper, we propose the fixed-order controller design method which only uses frequency response data of the plant. Moreover, the controller is designed by the convex optimization. Thereby, the identification cost is expected to be less than the previous method without an increase in the calculation cost. The effectiveness of the proposed method is verified through the experiment for the belt-driven two-mass system, and comparison with the previous method in the last of this paper.