Everyone has AHA! experiences such as finding innovative ideas when explaining our familiar things. The first objective of this research is to confirm the possibility of observing this phenomenon in laboratory settings. The second objective is to experimentally investigate how constraints given while explaining affect generation of innovative ideas. Basic design of our experiments comes from Finke's creative cognition approach. We conducted four experiments. The experimental results were analyzed through the comparison of the performance in the control condition and that in each of nine experimental conditions. In our experiments, in Phase 1, the participants were required to design furniture with a pencil and an experimental sheet, combining parts presented by the experimenter. In Phase 2, they explained their furniture under a certain constraint set up by the experimenter in the experimental conditions. On the other hand, in the control condition, they were required to consider innovative furniture instead of explaining their ideas. Last, in Phase 3, they were required to design new innovative furniture so that the effects of explanation in Phase 2 were investigated. The degree of creativity of each product was estimated with a 1 to 7 scale. The ANOVA showed that the degree of creativity of furniture designed in Phase 3 is greater than those in Phase 1 in both almost all experimental and control conditions; however gains from Phase 1 to Phase 3 in the experimental conditions did not exceed those in the control condition. Overall results indicated that it is relatively difficult to confirm effects of explanation in laboratory settings. However, only in one experimental condition where in Phase 2 the participants were required to explain their products as innovative furniture that is used for a different purpose from the original one considered in Phase 1, the gain exceeded that in the control condition.