There is a wide variety of vessel types in the transverse colon region. Among them, it is very rare that the accessory middle colonic artery(A-MCA)is branched from the splenic artery. We found a transverse colon cancer. The dominant vessel of the cancer was the A-MCA branched from the splenic artery. This vessel type was confirmed by preoperative 3D-CT. We performed a laparoscopic left hemicolectomy for the cancer. In this study, we report a case of safe laparoscopic surgery in which we separate the A-MCA branched from the splenic artery using the preoperative 3D-CT image.