In order to support the self-learning of the projection method in machine drawing, we have been developing the computer assisted instruction system which presents the 3-dimensional model reflecting mistakes in the projection. In this study, the system integrated a couple of functions, dealing with handwritten drawings and handling the two views as well as the three views, was implemented and a method to apply exercises for understanding the number of views in projection using the system was proposed. Since images provided to the system are taken by the camera of the user’s smartphone, one can easily obtain the images of drawings hiding either the top view or the side view. So that, the necessity of the third view in projection can be evaluated by comparing the 3-dimensional models generated by the two views and the three views. The proposed method is expected to usefully for learning of the third angle projection method in machine drawings with an active attitude.