To provide a pilaster which can lower the level of skills required for preparation of building materials and execution of construction, and can save labor required for the same.

Wall boards 1 are adjacently arranged at intervals. The pilaster 6a consists of a pillar fixing member 7, a pillar body member 8, and pillar edge members. A mounting portion 11 of the pillar fixing member 7 is mounted on a gap-side edge of the wall board 1. A bearing portion 12 of the pillar fixing member 7 is arranged on the mounting portion 11 and protrudes toward indoor side. A body covering portion 16 of the pillar body member 8 covers a part of the gap between the wall boards 1 from the indoor side. A body projection of the pillar body member 8 is formed on the body covering portion 16, which is detachably attached to the bearing portion 12. An edge covering portion of the pillar edge member covers an edge of the gap between the wall boards 1 from the indoor side. An edge projection 15b of the pillar edge member is formed on the edge covering portion to be detachably attached to the bearing portion 12. The edge covering portion of the pillar edge member covers an indoor-side surface of a longitudinal edge of the body covering portion 16 in a longitudinal direction over a desired length.