It is known that a servo system for step functions can be designed without using an integral compensator if the plant parameters are known accurately. Therefore, it would be desirable that an integral compensator is introduced only to obtain robust tracking ability while keeping the response for the nominal plant unchanged. From this viewpoint, this paper proposes a new method for designing a robust servo system which is optimal with respect to a quadratic performance index. The method uses the solution of a Riccati equation of order n, while many existing methods use the solution of a Riccati equation of order n + m, where n and m denote the order of the plant and the number of the plant inputs, respectively. It is also shown that, in our method, the circle condition can be always achieved at the plant input by suitably utilizing the design freedom, without changing the nominal response of the closed-loop system. Based on this fact on the circle condition, the connection with one of the existing design methods is also discussed.