To provide a heat insulating structure installed at an entrance of a cooling space to prevent air from flowing through the inside and outside of the entrance at a low cost with simple constitution.

A lower part of the entrance 18 is formed with an air curtain flowing in a horizontal direction by blowing air from an air blower 24 disposed at one side edge part of the entrance 18, from the one side edge part of the entrance 18 to the other side edge part facing the one side edge part, and an upper part of the entrance 18 is formed with a solid curtain with a plurality of louvers 40 hanging from the upper part of the entrance 18.