This study examined the relationship between Japanese language (JL) anxiety, beliefs about JL learning, and the amount of JL used in JL classes. The participants in this study were 670 undergraduate students studying JL at the Institute of Technology in Bangkok, Thailand, as compulsory subjects. A questionnaire survey was conducted, and a stepwise multiple regression analysis found that the amount of JL used by learners had a negative relationship with JL anxiety and a positive relationship with beliefs about JL learning and the amount of JL used by both native Thai and Japanese teachers. In addition, JL anxiety interacted with the amount of JL used by native Japanese teachers and beliefs about JL learning. JL teachers, especially native Japanese teachers, should attempt to reduce their learners' JL anxiety in order to maximize the effect of teachers' JL use and learners' beliefs and to support them in using JL more in classes.