In a floor panel provided with upper and lower members which have concave spaces and side surfaces having heights and are formed as a box shape, and structured such that the upper and lower members are combined up and down so as to communicate the respective concave spaces so as to form an internal space in an inner portion, the floor panel has a joint portion in which height leading end portions of the side surfaces of the upper and lower members are folded so as to enwrap each other so as to be connected, and the joint portion is arranged in a height midstream portion of the side surface of the floor panel, and is arranged at a position which is retreated to an inner side of the floor panel in relation to the side surface in both height end sides of the floor panel.