Inaction inertia occurs when bypassing an initial action opportunity has the effect of decreasing the likelihood that subsequent similar action opportunities will be taken. The primary purpose of this study was to examine the moderating role of individual difference of regulatory focus (promotion vs. prevention focus) on the inaction inertia effect. We conducted an experiment using a scenario in order to examine the proposed ideas. Subjects experienced regret higher when a more attractive previous opportunity was forgone rather than a relatively less attractive one. After missing a previous more attractive opportunity compared to the current opportunity, those in prevention focus experienced regret higher than those in promotion focus. When knowing the existence of the current opportunity, there was no significant difference between two groups of regulatory focus for missing a previous more attractive opportunity. When asking anticipated regret for current opportunity, those in prevention focus anticipated the same level of regret regardless of groups of difference in attractiveness. However, those in promotion focus anticipated regret higher when difference in attractiveness is larger than small. Further, anticipated inaction regret and valuation functioned as a mediator between the interaction of difference in attractiveness and regulatory focus and the likelihood to act taking the current opportunity. Several theoretical and practical implications were discussed based on those results.