A boarding and alighting support structure is applied to vehicle having a deck capable of boarding in a wheelchair. The boarding and alighting support structure includes a slope plate which projects obliquely from the boarding entrance end of the deck toward the ground, and a mounting member for installing the base portion of the slope plate at the boarding entrance end of the deck. The mounting member is configured to so that one end side is fixed to the base portion, other end is fixed to the entrance port end, and the one end side is flexibly configured with respect to the other end side.