To provide a heat insulation structural body which is excellent in workability and can maintain high fire resistance and high heat insulation property for a long period of time at low cost, and an external heat insulation structure of a building.

A heat insulation structural body comprises: a heat insulation member 11 with heat insulation property mounted on a building skeleton outdoor side 21a of a building skeleton 21, with one surface 11a of the heat insulation member 11 being opposed to the outdoor side 21a; a fireproof layer 12 which is a nonmetallic layer formed on the other surface 11b of the heat insulation member 11, with one surface 12a of the fireproof layer 12 being opposed to the other surface 11b; and a fireproof coating film 13 formed on the other surface 12b of the fireproof layer 12, with one surface 13a of the fireproof coating film 13 being opposed to the other surface 12b. The fireproof coating film 13 is expanded and carbonized by heat to form a fireproof heat insulation layer. Moreover, an outer heat insulation structure 20 of the building is configured by providing a heat insulation structural body formed in the above-described manner on the building skeleton outdoor side 21a of the building skeleton 21 of the building.