To provide an outside heat insulation method capable of forming an heat insulation layer 4 between a skeleton wall 1 and an insulating panel 2 without adding any swelling deformation to the insulating panel 2 by foaming pressure of a foaming thermal insulating material.

A panel supporting metal fitting 15 preventing the insulating panel 2 from making swelling deformation in the direction separating from the skeleton wall 1 is detachably mounted between the upper end section of the insulating panel 2 and the skeleton wall 1. Then, the foaming thermal insulating material is injected between the skeleton wall 1 and the insulating panel 2. After the injection, the panel supporting metal fitting 15 is removed.