PURPOSE: To provide a heat insulating panel used also as a form having local compressive strength and bending strength in which the adhesion between a foam consisting of a synthetic resin foamed body and a hardened concrete is enhanced.

CONSTITUTION: A foam 2 consisting of a synthetic resin foamed body has an irregular cut surface 3 on one side surface, a paper 4 is adhered to the other surface opposed to the one surface, and an aluminium foil is interposed between the paper 4 and the other surface to improve strength. When such a heat insulating panel 1 used also as form is manufactured, a thermal fusing adhesive 7 is interposed between the surface of the foam 2 and the paper 4 or aluminium foil surface, and they are pressed while adding a heat from the paper 4 side. When a concrete wall is constructed by use of the heat insulating panel 1 used also as form, concrete is placed on the irregular cut surface 3, whereby the heat insulating panel 1 used also as form remains in the state fixed to the concrete after the hardening of the concrete.