Clinical trials are prospective studies that evaluate the effectiveness of interventions on humans under certain circumstances. The frequentist approach in which the sample size is strictly controlled before tests is common in clinical trials. However, clinical trials that use an adaptive Bayesian method in which the trial can be flexibly stopped, based on data accumulated during the course of the trial, has been recommended to reduce costs and to meet ethical requirements in the fields of medicine and medical device development. In the field of psychological interventions, the current situation is that application based on Bayesian framework is often extremely poor. Therefore, this paper outlines the design method of clinical trials by the adaptive Bayesian method, discusses the benefits of and problems in its application to psychological intervention research, and provides examples of its virtual application.