An 81-year-old man visited his previous doctor with complaints of fever, vomiting, and diarrhea, and was transferred to our hospital on the 8th day after being admitted to the hospital for further treatment for a mass in the right side of his abdomen on CT. At the time of transfer, a fist-sized mass was palpable in the right side of the abdomen, but there was no tenderness, and blood tests showed that the white blood cell count was 10,700/μL and CRP 1.36 mg/dL, indicating a mild increase in inflammatory reaction. Contrast-enhanced CT showed an 8-cm diameter mass in the ascending colon with a stratified structure, and an antegrade intussusception with the mass as the advanced part. No intestinal obstruction was showed, and the contrast effect on the wall of the intestinal wall of the intussusception was favorable. Since the intussusception was already present on the previous CT scan, and since the patient also had severe aortic stenosis and a cardiothoracic examination was necessary, we decided on an elective operation. During the waiting period, lower gastrointestinal endoscopy revealed a type 1 tumor in the ascending colon, and biopsy revealed a highly differentiated tubular adenocarcinoma. The scope was not passed through to the oral side, and endoscopic repositioning was difficult. On the 19th day(12th day of admission), right hemicolectomy of the colon with D3 lymphadenectomy was performed. Since the descending duodenal wall was partially retracted into the area of the duplication, a partial resection of the duodenal wall was also performed, and the specimen was removed without releasing the duplication. Histopathologically, the tumor was diagnosed a 9.5×5.7 cm type 1 tumor with pT3, pN0, cM0, pStage Ⅱa(9th edition). The patient was discharged on the 9th postoperative day with good postoperative course.