Medial prefrontal cortex (MPFC) activation has been observed in studies of many types related to emotion regulation, self and familiar other-knowledge, mentalizing, morality, reward, and uncertainty. Furthermore, the anterior cingulate cortex (ACC) and the lateral prefrontal cortex (LPFC), which have reciprocal connections with MPFC, are considered necessary for cognitive regulation. Based on these findings, Nakao, Takezawa, and Miyatani (2006) proposed an integrative explanation for MPFC function: MPFC has a function of representing a benchmark that reduces conflict among many possible answers by biasing either choice of behavior. In this article, we review studies related to MPFC function and the benchmark hypothesis with recent new findings. Additionally, we discuss emotion regulation, which was not described in Nakao et al. (2006), in relation to the benchmark hypothesis.