To provide a simple building in which a decorative material can be easily mounted on a girder and fixed parts such as screws can be reduced.

An inventive simple building 1 includes a girder 5, a rafter 7, decorative materials 12, and 14 coating side faces of the girder 5, and decorative-material separation preventing members 23, and 43. The girder 5 has on its side faces locking parts 15, and 17 to which the decorative materials 12, and 14 are locked from the above, and the decorative materials 12, and 14 are locked to the locking parts 15, and 17 of the girder 5 from the above and mounted on the girder 5. The decorative-material separation preventing members 23, and 43 are mounted to an upper face of the girder 5, opposing the upper end of the decorative material 12 to prevent the decorative materials 12, and 14 from separating.