A 61-year-old man was referred to our hospital complaining of pancreatic tumor. Ultrasonogram (US) showed a tumor at the site of the pancreas body. The tumor was 40 mm in diameter, having a clear margin and a hypoechoic internal echo mixed with high echo areas, and the main pancreatic duct was not dilated. Additionally, the splenic vein was not depicted near the tumor, and collateral veins were found around the tumor on US. Laparotomy revealed that the tumor could be easily dissected from the pancreas but it was fused with the splenic vein. Excision of the tumor with the undetachable splenic vein was performed. The tumor was histologically diagnosed as leiomyoma of the splenic vein. Review of US showed the “beak sign” at the splenic vein, a finding that might be clue to help differentiate the site of the tumor.