Abstract: An object of the present invention is to provide an escalator installation method by which the installation operation can be conducted with the high operation efficiency and an escalator can be stably installed. In an architectural structure having a stairway, the present invention comprises: a first process for forming a lower pit in a lower floor positioned on the lower side of the stairway; a second process for forming an upper pit in an upper floor positioned on the upper side of the stairway; and a third process for accommodating a lower flat portion of an escalator constituted by an integral structure in the lower pit with the part of the stairway positioned between the upper pit and the lower pit being maintained so as not to be drilled, accommodating an upper flat portion in the upper pit, and setting an inclined portion of the escalator above the part of the stairs positioned between the upper pit and the lower pit.