A cold box is provided. The cold box includes an outer bag which is rectangular and has an upper opening, a lid which closes the upper opening of the outer bag, and a thermal insulator which is foldable and is detachably housed inside the outer bag. The thermal insulator is formed from a pouch-covered thermal insulation material. The thermal insulator includes a bottom wall, a top wall, a front wall, a rear wall, and a pair of side walls. Each of the side walls has a fixed part disposed adjacent to the rear wall and a turning part disposed adjacent to the front wall. The fixed parts are fixed to side faces of the rear wall, respectively, and the turning parts are rotatably coupled to front faces of the fixed parts, respectively. When the thermal insulator is folded, the front faces of the turning parts face each other.