To provide a heat insulating door having high strength of an installation part by firmly fixing a door closer, an upper frame, and an upper rail.

This heat insulating door connects the upper frame 10 and the upper rail 20 composed of an outdoor side metallic member and an indoor side resin member by the door closer 6 by housing a door body 2 composed of upper-lower rails and left-right stiles in a door frame 1 composed of upper-lower frames and left-right vertical frames arranged in a building opening part. A spacer 50 composed of resin is arranged in space parts 10c and 20e between the resin members 10b and 20b and the metallic members 10a and 20a in the upper frame 10 and/or the upper rail 20. The door closer 6 is fastened by a screw to the metallic members 10a and 20a via the spacer 50. A serially penetrating through-hole 20f is formed in an indoor side surface of the resin members 10b and 20b, the spacer 50, and the metallic members 10a and 20a. The door closer 6 is fixed by a screw 58 inserted into the through-hole 20f.