We investigated, through a cognitive psychological experiment and its protocol analysis, experts' and novices' interactive process between the mental operation by which participants considered their ideas and the external operations by which they actually produced physical objects in creative activity. In our experiment, the participants were required to build toy robots with creative features with LEGO Mindstorms. The experimental results showed that the experts could create work that fulfilled both high originality and practicality simultaneously. Moreover, the following four points were confirmed as characteristics of the experts' creative process: (1) the experts globally considered their initial ideas, (2) the experts predicted and considered their ideas by focusing on various aspects of important viewpoints, (3) the experts reconstructed their ideas more actively, and (4) the experts reconstructed their ideas by considering comprehensively the relationship among the elements constructing their plans.