To provide a method of constructing an access door capable of easily constructing the frame bodies or the struts of the access door without welding operation, easily adjusting the levelness and the heights of the frame bodies, and preventing the vibration of a water heater or the like from being transmitted to a living space.

This method of constructing an access door comprises a step of attaching stay members respectively having mechanisms for adjusting the dimensions of the vertical projections of the struts or the frame bodies installed at the nooks and corners of a space for covering pipes among those which are installed between the ceiling surface and the floor surface of a corridor so as to form the space, fixing the struts or the frame bodies by adjusting the stay members so as to press the ceiling surface and the floor surface, fixing rails to the struts or frame bodies so that the gaps are formed between the struts or the frame bodies and the ceiling surface and/or the floor surface so as to form a door frame, and attaching a door to the door frame so as to be opened and closed.