A floor panel structure of a vehicle body where a vehicle floor has floor panels with their peripheral edges linked to a plurality of frame members that are disposed in a vehicle body lengthwise direction and a vehicle body crosswise direction and linked to an engine or a suspension is disclosed. The floor panel has a joint where at least part of its peripheral edge is joined to the frame member, a groove formed along the entire length of the joint and a high-rigidity area formed within the low-rigidity area. The low-rigidity area forms a vibration blocking area along the entire length of the joint by using a difference in rigidity from the high-rigidity area.