PURPOSE: To increase the containing quantity of fish, to eliminate the overflow of water and to obviate a freezing vehicle at the time of transport by forming a heat beam reflecting layer on the inner and outer surfaces of a box and a cover, and freezing water immersed into fine fibrous material via pores opened at the heat beam reflecting layers.

CONSTITUTION: Fine fibrous material (a), and fiber slurry (b) in which water and paste are kneaded are press-fitted between a cavity 11 and a male mold 2. When filling of the fiber slurry (b) is finished, the air is blown from a pneumatic pressure blower into the air diffuser 21 of the male mold 2, and pneumatically molded. The water of the fiber slurry (b) is drained from a filter material 3 and a drain hole 21 out of a female mold 1 by the pneumatic feeding. Heat beam reflecting layera 6 of deposited films are formed on the whole inner and outer surfaces of a box 4 and a cover 5 molded in this manner, and pores 42, 52 which arrive at the fine fibrous material (a) by breaking the heat beam reflecting layers (films) 6 are opened at the superposed steps 41, 51 formed at the edges. The box 4, the cover 5 sufficiently immersed with water in the fine fibrous material (a) from the pores 41, 51 are contained in a freezing chamber, ice is frozen, and used as a fish box.