PURPOSE: To provide structure by which a conventional beam can be used even if an interval between columns is lengthened, by a method wherein a beam with integral times the length of architectural modules is spanned between the columns neighboring with each other, which have the interval of integral times the length of the architectural modules and additionally of a length of α, and protrusions, each of which protrudes from the side of the column opposed to the end part of the beam by the length of α, are connected with the end parts of the beam and are fastened to each other.

CONSTITUTION: An interval L between columns 2, 2, in which a beam 1 is spanned, is set to integral times the length of architectural modules and additionally to a length of α. A length W' of the beam 1 to be spanned between the columns 2, 2 neighboring with each other is set to integral times the length of the architectural modules. The length of a protrusion 3 protruding from each of the columns 2 is made the same as the length of α. In this way, even if the interval L between the columns 2, 2 is made longer than the length W' by the length of α, the end parts of the beam 1 each are connected with the protrusions 3, and the beam 1 composed of the length W', which is integral times the length of the architectural modules heretofore in use, can be set-up without lengthening the length of the beam 1.