Appendiceal diverticulum is rare. We encountered a case of appendiceal diverticulum with chronic appendicitis. A 56-year-old man presented to our hospital with right lower abdominal pain. An abdominal computed tomography (CT) scan showed swelling of the appendix body and the wall thickness of the base of the appendix. Due to the possibility of appendiceal tumor, we performed a laparoscopy-assisted ileocecal resection with lymph node dissection. The appendix had a diverticulum with chronic inflammation, but it did not have a neoplastic lesion.