When they use daily electronic appliances to achieve their goals, users need to decompose their goals to a set of subtasks in a specific way. A previous study revealed that users who have extreme difficulties in using such appliances fail to decompose the task, or that their decompositions are different from the one that designers assume. Based on this view, we propose a new method to help users understand “task decomposition” by providing all operating functions in a tree structure. We conducted three experiments. In the first and second experiments, we built support panels corresponding to the operating panels of two different copiers, which visualize all operating functions of respective copiers to facilitate users' understanding task decomposition. We compared the copying performance of subjects who used the support panels with that of those who did not. Both the support panels were found to be useful for technologically inept users. We then built an interface by integrating the operating panel into the support panel, both of which were provided in the first experiment: We conducted an experiment similar to both of the previous ones and evaluated its effectiveness. The result showed that this interface facilitated users' task decomposition. We conclude that the supporting method we proposed is effective for technophobic users' understanding task decomposition.