We evaluated the significance of the success rate of breast conserving surgery in patients with breast cancer discovered by using different screening methods. Patients underwent either population-based screening (group A) or opportunistic screening(group B). We retrospectively investigated patients who visited our hospital in 2012. A total of 552 patients visited our hospital for breast cancer screening. Thirty-five percent of these patients were diagnosed with breast cancer based on the histopathological results. The rate of breast cancer discovery was significantly higher in group B than in group A. The rate of discovery of early clinical stage breast cancer was also higher in group B than in group A. The rate of total breast conserving surgery for breast cancer screening cases was 54.4%. The rate of breast conserving surgery was higher in group B than in group A. Group A patients only underwent mammography, while 80.1% of group B patients underwent mammography plus ultrasonography. These results suggest that adding ultrasonography to breast cancer screening is useful for detection of early breast cancer.