Contrary to the image of an egalitarian society, the number of irregular workers in Japan is increasing, and temporary workers in particular have gathered public attention since 2008, when a 25-year-old male temporary worker went on a daytime stabbing rampage in Tokyo with seven people killed and ten people injured. By doing an academic literature review on the dual structure between large firms and small- and medium-sized enterprises (SMSEs), the emergence of irregular work, and the welfare system in Japan as well as analyzing the content of 10 interviews with representatives of Community Unions that support irregular and SMSE workers in Japan, this study examines: what labor issues irregular and SMSE workers in Japan pose, how effectively labor unions are able to support and mobilize irregular workers, and what improvement needs to happen in the welfare system in Japan to adapt to the changing employment landscape in Japan. The analysis of academic literature revealed that a gender bias exists in the irregular labor market of Japan, the labor unions in Japan are organized mainly in large enterprises and are exclusive to irregular and SMSE workers, and business enterprises played a major role in maneuvering the welfare system in Japan. However, the interview materials with Community Union leaders show that it is not so much gender but industrial labor demographics that lead to a discrepancy between female and male workers with volatile employment. Community Unions are wiling to help irregular and SMSE workers through troubleshooting activity, bargaining against managers, and lawsuits. At the same time, they have difficulty in mobilizing irregular and SMSE workers because a large number of workers who talk to Community Unions about labor issues do not sign up for membership in a Union. Welfare programs in Japan are badly designed for male irregular and SMSE workers because employment insurance gives them only a symbolic benefit. Being in the status of 'dependents,' male workers with volatile employment are not able to design welfare programs of their own accord. The state has begun to deregulate the eligibility for employment insurance, and therefore it is hoped that the conditions on employment insurance may be relaxed further.