The pilot reported that he extended the landing gear prior to the landing and observed that the gear down light was illuminated. The pilot described the touchdown as “soft.” However, during the roll out, the nose gear collapsed followed by the left main gear and the right main gear. The airplane came to rest on the underside of the fuselage on the runway. The pilot shutdown the airplane and the occupants egressed from the airplane without further incident. The air traffic control tower controller observed the airplane during the landing roll and reported that the airplane’s landing gear was down. The airplane sustained substantial damage to the underside of the fuselage. Due to the damage sustained to the landing gear system gear box and swing doors components, a postaccident functional test of the electric gear system could not be performed. The landing gear was able to be extended manually.