Recently, Inner Strength (IS) has been increasingly focused as a personal resource that helps people overcome adversities and promote well-being. The purpose of this study was to develop a Japanese version of the IS Scale (ISS-J) based on the ISS of Lundman et al. (2011), which consists of four factors: Firmness, Creativity, Connectedness, and Flexibility. Moreover, reliability, construct validity, and criterion related validity of the Japanese scale was investigated. Japanese college students (N=395) participated in the study. Results of exploratory factor analysis indicated that ISS-J comprised three factors with the exception of Flexibility in ISS: Creativity, Firmness, and Connectedness. Cronbach's alpha values indicated adequate internal consistency of the ISS-J (α=.79–.88). Confirmatory factor analysis using structural equation modeling demonstrated sufficiently high validity of the three-oblique-factor model of the ISS-J. Additionally, there were significant and positive correlations between ISS-J and the Sense of Coherence and Self-Esteem Scale scores respectively (r=.24–.50, p<.001). These findings indicate that ISS-J has adequate reliability and validity. It is suggested that further studies are needed to examine the reliability and validity of the scale with other age groups.