© 2018 The Authors The results of several epidemiological studies have shown a moderate association between postpartum depression (PPD) and mother-infant bonding (MIB); however, associations and changes that longitudinally considered parity were not reported. We investigated the possible association between PPD and MIB at one month after birth, in addition, the changes of these indices by parity. From a dataset comprising 103,099 maternal registrations in The Japan Environment and Children's Study, the present study analyzed complete data on questionnaires for 76,363 women who participated once (cross-sectional group) and 3753 women who participated twice (follow-up subgroup). Edinburgh Postnatal Depression Scale (EPDS) scores and the Mother-to-Infant Bonding Scale-Japan (MIBS-J) scores were obtained one month after delivery. We identified the two factors of the MIBS-J, “lack of maternal feeling (LMF)” and “anxiety about caregiving (AC)” through confirmatory factor analysis. Associations between total EPDS and each factor of MIBS-J were evaluated using multiple regression analyses after adjusting for potential confounders. Total EPDS and both factors (LMF and AC) were positively related in the cross-sectional group (fully adjusted β = 0.26 and 0.39 for LMF and AC, respectively), in the follow-up subgroup at first participation (0.24 and 0.40, respectively) and at the second participation (0.25 and 0.39, respectively). Multiple regression analyses revealed a robust, moderate relationship between postpartum depression and mother-infant bonding. PPD and MIB scores were shown to decrease from the first child to the second in the follow-up subgroup. Consequently, interventions which would increase a mother's child care experience and expertise would prevent PPD and improve MIB.