To produce an inexpensive heat insulating causing no discoloration with time by applying an antimicrobial mildewproofing paint causing no discoloration with time to the inner surface of an inner box or adding an antimicrobial mildewproofing agent causing no discoloration with time to the inner box.

This heat insulating case comprises an inner box, an outer box and a foamed heat insulating material. An antimicrobial mildewproofing paint causing no discoloration with time is applied to the inner surface of the inner box or an antimicrobial mildewproofing agent causing no discoloration with time is added to the inner box. A zinc based or copper based inorganic antimicrobial mildewproofing paint is preferably employed. Since no silver based antimicrobial mildewproofing agent is employed, an inexpensive heat insulating case causing no discoloration with time is obtained. An organic antimicrobial mildewproofing paint or a composite paint thereof with a zinc based or copper based inorganic antimicrobial mildewproofing paint may also be employed.