This paper concerns the design method for the controller of structures arranged in parallel. In the case of vibration control for 1DOF-1DOF model structures, the authors previously proposed the method of vibration control to individual structures without addition of mass like active dynamic absorbers. This paper shows the design method for a controller of 1DOF-1DOF parallel structures by the LQ theory. First, the relationship between dimensional and nondimensional parameters in the LQ theory can be determined by the similarity law. The characteristics of the controller are then analyzed, and from this, it is easy to design dimensional parameters of the controller. Subsequently, it is demonstrated that there is an optimal weight matrix for the characteristics of the controller, and this optimal weight matrix and its roots are analyzed. Furthermore, the influence of structural parameters to vibration control is shown by simulation. It is demonstrated theoretically that this method is effective for the design of 1DOF-1DOF parallel structures.