An “incubation period” refers to an individual’s temporary shift away from an unsolved problem, which ultimately facilitates better problem solving. In this study, we experimentally examined whether creative problem solving was facilitated in accordance with the frequency of mind-wandering during an incubation period. Fifty-nine Japanese undergraduate participants (23 men and 36 women) were asked to complete the Unusual Uses Test (UUT) twice; the UUT is a traditional measurement of the various aspects of divergent thinking (including fluency, flexibility, and originality). They were also asked to rate the frequency in which they engaged in mind-wandering during the interval between UUTs, which was considered as the incubation period. The results indicated that participants who reported a higher frequency of mind-wandering during incubation exhibited more creative solutions on the UUT, especially in terms of flexibility and originality, than did those reporting a lower frequency of mind-wandering.