The pilot reported that the accident occurred during landing at the intended destination airport under visual weather conditions and light winds. He stated that upon landing, the left main landing gear collapsed and the left wing contacted the runway. The airplane subsequently departed the runway pavement and came to rest about mid-field in the grass adjacent to the runway. It had rotated about 180 degrees and was oriented on an approximately reciprocal heading. The right main landing gear also collapsed during the accident sequence. The pilot stated that verifying the landing gear indications was normally part of his before landing procedure. However, he could not specifically recall observing three green indications prior to the accident. A post accident examination revealed substantial damage to the lower fuselage in the vicinity of the cabin entry door. In addition, the inboard landing gear doors exhibited crushing damage consistent with the landing gear being in transit at the time of contact with the runway. The inboard landing gear doors open when the gear is in transit and close after the gear extension sequence is complete. Recorded winds at the time of the accident were 8 knots.