To reduce manufacturing cost by eliminating a step of bonding a heat insulating material to a rising part.

A form holder 2 includes: a base part 21; a first support part 25 which is installed to the base 21 and supports the lower end of an outer frame plate 50 in a state where the outer frame plate 50 is erected; a leg part 26 which is erected on the base 21 with a space from the first support part 25; a second support part 28 which is installed to the upper end of the leg part 26 and supports the lower end of an inner frame plate 51 in a state where the inner frame plate 51 is erected; and a receiving part 33 which is installed to the upper end of the leg part 26, extends from the second support part 28 to the first support part 25, and receives the lower end of a heat insulating material 7 to support it from below.