To provide an assembling method which enables the easy and safe construction of a working booth with a high ceiling.

This assembling method comprises: a step of forming an upper structure 10x composed of a ceiling section 10c and an upper wall section 10w as upper sections of the working booth 10, by vertically and horizontally combining a plurality of pieces 11a, 11b and 11c of bar stock in the same cross-sectional shape on a floor surface F as an installation-planned surface, fixing end surfaces of the pieces 11b and 11c of bar stock to an outer peripheral surface of the another piece 11a of bar stock by means of a connecting implement 26, and fitting panel materials 14 and 15 into an area enclosed with the pieces 11a, 11b and 11c of bar stock; a step of lifting the upper structure 10x up to a fixed height by hooking a hook of a lift 50 to an engaging implement of an engaging member attached to a lower edge corner portion 10d of the upper structure 10x; and a step of forming a lower wall section as a lower section of the working booth 10 at the lower edge of the upper wall section 10w of the lifted upper structure 10x by means of the piece 10d of bar stock and the panel material 14.