The variable substitution is an important mean of the problem solving. Nevertheless, the discussion for the variable substitution has been inadequate until now. Thus we tried to form foundation on the use of variable substitution in teaching and learning mathematics by discussing about the variable substitution. We tried to consider the role of variable substitution in learning mathematics in the pursuit of this purpose. As a result, we could analyze the role of variable substitution in various contexts. At first, the variable substitution is a mean for insight into the structural similarity in the similar problems. Next, the variable substitution is a mean for diversion of viewpoint. It is not easy for novice students to cognize a complex expression as a procept without the variable substitution. But teachers who already are familiar with the variable substitution do not know the difficulty of this. And there can be the conflict between teachers and students. Thus it is required to make a good use of the variable substitution in the school mathematics.

variable substitution, structural similarity, diversion of viewpoint.