A 53-year-old woman with recurrent abdominal pain was referred to our hospital. Based on the enhanced abdominal computed tomographic (CT) finding, she was diagnosed with intussusception of the sigmoid colon. Colonoscopy was performed to release the intussusception, and a lead point lesion was detected. An advanced cancer was found in the rectum, which could be pushed back into the sigmoid colon easily using pressurized air. A more-advanced colon cancer was also detected on the oral side of the lesion. The patient was diagnosed with double cancer of the sigmoid colon and was treated with laparoscopic sigmoidectomy with lymph node resection (D3). Preliminary reduction by colonoscopy prior to surgery is an effective option in cases of adult intussusception. Colonoscopy can be used to perform definitive and qualitative diagnoses.