To provide a half-precast concrete board with high strength which simplifies bar arrangement operation by using a spiral hoop, and is resistant to an external force from an upper or lateral side.

This half-precast concrete board comprises: an upper chord reinforcement, and first and second lower chord reinforcements which are parallel to one another, and are positioned at apexes of triangles in a longitudinal view; the spiral hoop which is wound around the upper chord reinforcement, and the first and second lower chord reinforcements; a mesh reinforcement which is positioned between the upper chord reinforcement, and the first and second lower chord reinforcements, and is elongated in a plane parallel to the upper chord reinforcement, and the first and second lower chord reinforcements, and binds the spiral hoop to the upper chord reinforcement, and the first and second lower chord reinforcements; and the concrete board on which the upper chord reinforcement, a part of the spiral hoop and the mesh reinforcement are exposed, and in which the rest of the spiral reinforcement and the first and second lower chord reinforcements are embedded.