This study aims to show the relationship between emotion regulation and Warabe-uta, also to consider the knowledge of childcare by focusing on baby’s positive emotion. Warabe-uta is a Japanese traditional children’s play song. Nursery teachers often sing Warabe-uta for baby’s in order to regulate their emotion. Some research considered the value of Warabe-uta as a music teaching material. However, a few studies investigated the relationship between Warabe-uta and emotion regulation. In this study, therefore, I analyzed positive emotion regulation of a baby who has problem in relationship with others through 4scenes by singing a Warabe-uta. As a result, I found that, Warabe-uta effect baby’s “intentionality” “embodiment” “responsiveness”, and also on nursery teacher’s “intentionality” “embodiment” “nursing characteristic”. It prompts a positive emotion regulation in baby. This result might have positive effect on inter-subjective connection, but in contrary, it might make baby to be dependent on her own nursery teacher. It is interpreted from this study that relationship between emotion regulation and Warabe-uta is close. It is important that nursery teacher work to cooperate for baby’s development.