The present invention relates to a door that has a sufficient strength against bending and is not damaged by moisture. Front and rear plates 10 and 20 of the door of the present invention are made of a glass fiber material. A pair of transverse frames 30a and 30b made of synthetic resin and the a pair of longitudinal frames 40a and 40b made of lumber comprising bonded sheets of veneer are fixed to edge portions of the front and rear plates therebetween. Upper and lower frames of the longitudinal frames are fixedly bonded to bottom and top surfaces of the respective transverse frames so that they cannot be exposed to the outside. Further, a pair of covers 50 made of synthetic resin are attached to outer side surfaces of the longitudinal frames so that the longitudinal frames cannot be exposed to the outside. An inner space defined by the frames between the front and rear plates is filled with a foaming liquid to form a foam layer.