A wing lock structure includes: a block provided to a side gate, and provided with a plurality of convex portions that are convex in a width direction of a vehicle and concave portions that are concave in the width direction of the vehicle in a longitudinal direction of the vehicle; a wing plate provided at a predetermined portion of a wing side panel facing the block in a closed state and having irregularities corresponding to the concave portions and the convex portions on a surface that comes into contact with the block; and a pressure contact portion that presses the wing plate to bring the wing plate and the block into contact by pressure.