A partitioning member having therein a space is provided at the opening of a thermal insulation box having an outer and inner boxes forming a space in between said outer and inner boxes. The two spaces communicate with each other and filled integrally with a thermal insulation material by injecting into the space between said outer and inner box an expandable thermal insulation material, which diffuses into the space inside said partitioning member, to thereby provide in a simple and economical way a thermal insulation box having a small number of components but as uniform thermal insulation.