To provide a xonotlite based calcium silicate lightweight panel whose inside is provided with a reinforcing material such as a reinforcing rod in which a heating dimensional change and thermal shrinkage are reduced for further improving its heat resistance, and to provide its production method.

A calcareous raw material composed of portland cement and quicklime, a siliceous raw material and plaster are blended in such a manner that the molar ratio of CaO/SiO2 is controlled to 0.8 to 1.1, and also, the atomic ratio of Al/(Al+Si) is controlled to ≤6%. The blend is mixed with water, so as to be slurry. Metal aluminum powder is added to the slurry, so as to obtain a molding material. The molding material is cast into a molding flask at which a reinforcing material is beforehand arranged, is subjected to foaming-hardening treatment, and is subjected to steam curing treatment.