Abstract: A building panel formed by extruding a mixture of wooden and/or bamboo powder and a binding agent. Its panel body comprises (i) a door panel extending in the direction of extrusion, (ii) a pair of longitudinal frame members formed in the direction of extrusion on the right and left sides of the door panel, and (iii) a panel strip formed in the direction of extrusion at the center of the door panel. The door panel, the paired longitudinal frame members, and the panel strip are formed as a single piece. The door panel and the panel strip are cut short at their upper and lower ends so that the upper and lower ends of the longitudinal frame members stand out beyond the cut ends of the door panel and the panel strip, the standing-out portions constituting tenons.