By using unique survey data, we conduct a detailed study of the gender salary gap within economics departments in Japan. Despite the presence of rigid pay scales emphasizing age and experience, there is a 7% gender salary gap after controlling for rank and detailed personal, job, institutional and human capital characteristics. This gender salary gap exists within ranks. We find no gender promotion differences. In addition, we find a concentration of the salary gap in public universities and in research oriented universities. Our results show no evidence that the gender salary gap is reducing over time, and reject the hypothesis that females' choice between household work and market activities is responsible for the gender salary gap. (Contains 7 tables and 2 figures.)