This technical note deals with analysis of fundamental limitations for SISO systems in tracking control problems. In the existing results, the fundamental limitations are analyzed based on detailed assumptions of reference signals such as the step, the trigonometrical signals and so on. On the other hand, we define a class of reference signals in an abstract but general manner. For the general class of reference inputs, we give the analysis of the tracking performance limitations based on the achievable set of the outputs. The analysis results can separate the contributions of the plant and the reference signal clearly.