The theory of planned behavior has explained various involvements in activities such as hobbies and sports on the basis of the cost–benefit approach. To evaluate the mechanism of participation in volunteer activities, we applied the theory of planned behavior, as well as a basic model using elements of potential volunteers’ demographics and psychology, to volunteer activities. Data were obtained in two Japan-wide surveys conducted in 2019 and 2020. The model of planned behavior described intention to participate in volunteer activities relatively well but did not predict actual participation. Both the model of planned behavior and the basic model found only weak factors associated with participation in volunteer activities. These results indicate that the mechanism of participation in volunteer activities differs from that of usual behaviors, for example, leisure activity participation. Strategies for recruiting volunteers should account for these differences.