On September 15, 2005, at 1100 Pacific daylight time, a Beech 95-B55 (Baron), N127F, landed with the gear retracted at Porterville Municipal Airport, Porterville, California. The airplane was registered to a private company and was being operated by the pilot under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, was not injured; the airplane sustained substantial damage to ribs in the fuselage belly. The pilot departed from Big Piney - Marbleton Airport, Big Piney, Wyoming, at 0700, and was landing at his destination when the accident occurred. Visual meteorological conditions prevailed and a visual flight rules (VFR) flight plan had been filed. According to the pilot, he entered the landing pattern for runway 12, which was the active runway in use. After the pilot was established in the pattern, the wind changed and an airplane departed runway 30. The pilot decided to change his landing pattern for runway 30 and crossed midfield where he entered the downwind leg of the traffic pattern for runway 30. Upon entering the downwind leg of the traffic pattern for runway 30, the pilot retracted the landing gear to decrease the required engine performance for the airplane. The pilot turned base and then final while extending the flaps and failed to lower the landing gear. He stated that he landed the airplane with the landing gear in the retracted position. No mechanical anomalies were reported.