Smart device appeared as IT technology develops and it caused the proliferation of digital contents. It is because that App technology supports to install and use the contents in the smart device easily. App is developed by the creativity and the programming skill and the commercial value is generated in the process of development. In this paper, we taught how to develop APP to elementary school students by Android App Inventor program and observed the changes of their thinking through reflection-note which describes thinking of them. This research was carried out for 28 elementary school students, 5th and 6th grade. We found the attitude that students try to solve problem actively with the high interest. They enjoy showing developed App to others easily and quickly, which is the characteristic of smart devices. We also found a phenomenon that the students consider commercial value.