A role of models in scientific explanation and insufficiency of unification view of explanation are discussed. Model is constructed by abstracting some important elements from the real world. There are too many complicated interactions in the real world to calculate, but model makes calculations possible. However, that is only part of importance of model in scientific activity. At the first sight, we think that it is better for scientists to use models including more elements (it means the model is closer to the real world), than to use models with less elements. Nevertheless, even when scientists can calculate by using more complex models, they usually use more simple models. This fact gives us the key to clarify an important role of models in scientific explanation. In this presentation, I would like to show that using simple models as possible makes it possible to explain phenomena thus only achieving unification is insufficient for explanation.