Recently, the religious activity of prayer has been the subject of scientific research. However, the results have been poor in terms of reproducibility, which demands that a more limited approach to investigating prayer be adopted. This study examined the Japanese custom of holding up the hands in prayer (sazuke) among 296 devotees of Tenrikyo (a large religion) with respect to the participants’ mental health. We dopted the subjective well-being scale of Ito et al. (2003) and applied the SD method by means of a questionnaire among the devotees. We subjected each extracted factor to multiple regression analysis. Our results showed that sazuke prayer enhanced the factors of “intrinsic sense,” “self-evaluation,” and “confident sense of fulfillment” in the well-being scale of the participants. Thus, the act of prayer appeared to augment the subjects’ positive and spontaneous feelings in addition to promoting their self-confidence.