This three-year prospective study on the effects of job stress on depressive symptoms over time was conducted among male blue-collar workers in an electrical factory in Japan. Data were collected at yearly intervals by means of postal questionnaires. Initially ten job stress variables, five major covariates, and depressive symptoms (Zung Self-Rating Depression Scale) were measured. In the yearly examinations, depressive symptoms were measured for a total of 468 respondents. The results indicated that job unsuitability was a significant predictor of depressive symptoms in the second and third year, after control for the initial covariates and depressive symptoms. Lack of control over workplace and poor human relations at the workplace were significantly associated with depressive symptoms after one and two years, respectively. Job unsuitability and poor human relations at the workplace seem to be risk factors for long-lasting depressive symptoms in Japanese blue-collar workers.