This paper examines the hypothesis for internalization of irregular employment by the original data of more than 3000 non-regular and unmarried individuals. The previous dual labor market hypothesis claimed that irregular workers belong to the secondary market: they lack of on-the-job learning opportunities, and earnings do not reflect ability and experiences. However, our study finds a positive correlation between working years and annual payment even for atypical workers. And their payment reflects previous experiences of regular employees. These results suggest that not a small proportion of irregular workers are actually treated as the lower tier of internal labor market.