Postpartum depression is a serious problem not only for mothers, but also for their children and families. Evidence is scarce on the effectiveness of couple-targeted antenatal interventions aimed at preventing postpartum depression in Asia. Therefore, we implemented an antenatal parenting support program from Australia ("empathy program") at three sites in Japan, and assessed the characteristics of participating couples and changes in their mental health indicators before and after the program (during pregnancy and 6 weeks postpartum, respectively). In this program, participant couples discussed concerns during pregnancy and a "difficult day" scenario with other same-gender participants and then with their own partners. In total, 100 couples attended the program. Among 60 participating mothers, 20% screened positive for maternal depression symptoms (defined as an Edinburgh Postnatal Depression Scale greater than 9). Changes in paternal empathy and maternal antenatal Edinburgh Postnatal Depression Scale score were significantly associated with maternal postpartum Edinburgh Postnatal Depression Scale score in multivariable analyses. Our results indicate that a key in preventing postpartum depression is paternal involvement and long-term support from antenatal phase.