Abstract Background: In Japan, national health insurance covers medical treatments that are designed to help quit smoking. However, some people do not undergo necessary smoking-cessation treatment, despite it being available through their health insurance. A major contributing factor to this is considered to be an individual’s readiness to quit smoking (e.g., no intention to quit smoking, planning to quit smoking eventually, or ready to quit smoking immediately). Readiness to quit smoking significantly influences the balance of the decision-making process in terms of the pros (advantages) and cons (disadvantages) of smoking; however, there is no standard scale that measures the balance of smoking-related decisions. Accordingly, we created a Japanese-language version of Velicer’s Decisional Balance Scale (hereafter referred to as the Japanese version of the Smoking Decisional Balance Scale) in this study and then analyzed its reliability as well as validity. Methods: For this study, we conducted an online survey of 807 individuals. Study I included an item analysis of the newly created Japanese version of the Smoking Decisional Balance Scale. Study II clarified the factor structure of the Japanese version of the Smoking Decisional Balance Scale and verified its reliability and validity. The questions consisted of items from the Japanese version of the Smoking Decisional Balance Scale and items intended to classify stages of behavioral change. Results: The item analysis in Study I showed no ceiling/floor effects in terms of the items of the Japanese version of the Decisional Balance Scale for smoking. The factor analysis of the Japanese version of the Smoking Decisional Balance Scale in Study II extracted two smoking-related factors—pros and cons—that are similar to the original version of the scale. The internal consistency of each factor is high. In addition, the scores for the pros and cons of smoking changed significantly at each stage of behavioral change. The results are consistent with previous studies, confirming the construct validity of the Japanese version of the Smoking Decisional Balance Scale. Conclusion: The present study reveals that the Japanese version of the Smoking Decisional Balance Scale has high reliability and validity. The study demonstrates the possible application of the scale to smoking-cessation support and treatment.