The purpose of this study was to compare the improvement in skill with and without immediate image feedback during the learning of a sidearm throw in flying disk sports. We utilized the Dart Trainer Pro application program (Dart Fish Co. LTD) in a personal computer; this program has a feature of delayed image playback. Using a digital video camera, we recorded the throwing motion of students who attended the sports classes at Keio University; among them, few students who were included in the image feedback group, and they immediately watched their respective images on a computer screen. The aim of all the students in the class was to acquire the skill of throwing using a straight disk by a sidearm throw. According to the results, the success rate of throwing a straight disk and self-evaluation for the acquisition of skill in the image feedback group were higher than those observed in the group that did not receive feedback. It was confirmed that immediate image feedback was very effective in improving the throwing skill. In addition, by using the analytical function of Dart Trainer Pro, we demonstrated an instance of improvement / non-improvement in the throwing skill depending on the motion. The next issue in the future to construct a more effective teaching program that combines image feedback and the teaching-matched skill pattern by using such motion examples.