We devised the science class using the transparent round shape water tank in the unit of "the function of running water" for the fifth grade of elementary school and practiced it. From a point of view that we control a condition and examine, the aim that we introduced a transparent round shape water tank into the unit is to observe the movement of sand grains carefully and to consider the change of the sand bed form in connecting with the number of times of stir to make water flow. This experiment can be carried out easily without special preparations. The children were able to perform experiments with interests, and to aware of the change in sand bed. Significance to introduce the experiment into the unit rises more by devising consideration of contents.