The aim of this study was to develop a Japanese version of the Game Addiction Scale (GAS7-J) and investigate its validity and reliability. The GAS7-J was translated using back translation. In the study, 352 Japanese adolescents responded to a questionnaire which included the GAS7-J. Factor analysis revealed a factor structure similar to the original scale, with higher internal consistency. Additionally, the GAS7-J correlated with both time spent on games and loneliness to a similar degree as in a previous study. In conclusion, the GAS7-J has an acceptable level of validity and reliability.