On July 16, 1993, at 1945 Pacific daylight time, a Piper PA39, N8975Y, sustained a complete landing gear collapse on the landing roll out at Thermal, California. The pilot, who was under going a multi engine land airplane class rating check ride, had intended to retract the flaps, however, moved the landing gear selector handle to the UP position instead. The aircraft was operated by Proflight, Inc., of Las Vegas, Nevada, and was rented by the pilot for the instructional flight. Visual meteorological conditions prevailed at the time and no flight plan was filed for the operation. The aircraft sustained substantial damage. The certificated private pilot and the designated pilot examiner were not injured. The flight originated at the Palm Springs, California, airport on the day of the mishap at about 1830 as a local area pilot certification check ride. In a telephone interview, the pilot examiner stated that the applicant pilot had been flying a Piper PA23-160 for his multi engine training. The PA23 cockpit is set up with the landing gear selector handle on the right side of the power quadrant and the flap selector on the left. The PA23 was in the maintenance shop and the applicant was given the Piper PA39 for his flight test. The PA39 cockpit is set up with the landing gear selector handle on the left side of the power quadrant and the flap selector on the right. The examiner stated that during the traffic pattern he personally checked that the landing gear handle was in the DOWN position, with three green indicator lights. The aircraft made a normal landing. The examiner said his attention was distracted momentarily by locating the radio microphone, and, when he looked up again, the aircraft was settling down on the runway with the landing gear selector handle in the UP position. According to the pilot's statement, he said that he was reaching for the flap handle to retract the landing flaps and mistakenly moved the gear handle instead.