This study examined the psychological status of Japanese ambulatory patients with primary breast cancer, with a focus on evaluating the impact of the patients’ self-repressive trait and the role of previously identified associated factors, including social support, attributes, and disease-related variables. The subjects included 112 women [mean (SD) age: 58.3 (12.7)] in Japan with postoperative primary breast cancer. The results showed that around 40% of the subjects were in a psychologically vulnerable situation. In addition, the self-repressive trait and support from family were significant predictors of both anxiety [self-repressive trait (β = 0.30, p = 0.000) and family support (β = -0.37, p = 0.001)] and depression [self-repressive trait (β = 0.26, p = 0.002) and family support (β = -0.42, p = 0.000)], whereas attributes and disease-related variables were not. Health care providers need to recognize that self-repressive patients may seem to be well-adjusted when, in fact, they are suffering. Careful assessment of self-repression and psychological status is needed. Family support can contribute to a better psychological status of patients. Nurses need to encourage and provide support for not only the patients but also the family members so that family members can also effectively care for the patients’ needs.