PURPOSE: To provide a building having simple construction, excellent durability and degree of freedom of arranging rooms by composing a strut structure of a building pillar unit group consisting of statically determinate structures having one cross beam and two fulcrums.

CONSTITUTION: A building support pillar A' is composed by providing a building pillar unit section A meter moduled from a statically determinate structure jointed with one beam and two fulcrums in a measure-like fashion as viewed in a plan on a foundation section 5 to compose a building support pillar A'. The respective adjacent building pillar unit sections A are connected to each other by a connecting beam material 6 to define a space for arranging a square room as viewed in a plan.