Breast cancer in male is comparatively rare. We encountered a case of breast cancer in an elderly male who was treated with consideration of age. A 78-year-old male consulted our hospital with a lump on his right breast. The tumor was 3 cm in diameter and was palpable in the E area of his right breast, accompanied by pain. Mammography showed an indistinct mass in the S area. Ultrasonography revealed a well-defined and rough, lobulated mass. Core needle biopsy was performed, and the pathological diagnosis was invasive ductal carcinoma. Metastatic work-up revealed no evidence of metastasis. The patient underwent mastectomy with sentinel lymph node(SN)biopsy and axial lymph node dissection(Ax)because of positive metastasis in an SN. The pathological findings from the surgically resected specimens indicated solid-tubular carcinoma. Lymph node metastases were observed in an SN(1/1)and Ax(1/3). On immunohistochemistry, tumor cells tested positive for estrogen and progesterone receptors and negative for HER2/neu protein expression. The Ki-67 labeling index was 14%. Postoperatively, the patient has not received chemotherapy, but received hormone therapy as adjuvant therapy considering his age. Nine months after the surgery, the patient is well, and metastasis has not appeared.