In this paper, a trade-off analysis in a design problem of a Two-Degree-of-Freedom controller, in which a feedback controller and a feedforward controller share common dynamics is considered, and a design method for the TDF controller is proposed. The design problem of the TDF controller is formulated as a simultaneous optimization problem for these two controllers. Specifically, the problem is formulated as the non-standard H_∞ control problem in which a subsystem from the external input to the measurement output is column full rank. By this formulation the TDF controller can be derived through a one-step design process. As a result, the computational time can be reduced, and the controllers, which share common dynamics, are designed with lower order than those designed with a two-step design process based on the standard problem. Furthermore, a reduced order controller, which has lower order dynamics than a generalized plant has is derived by using free parameters of the general solution.