To allow a reactor vessel or the like to be filled with water without generating a cavity between tightly arranged facility equipments even in a body to be cut incorporating congested facility equipments and to perform a stable cut by freezing it.

A coolant pipe 5 is wound around the outer surface part of a pressure vessel 1 in a coil shape, and the start end and terminal end thereof are connected to a refrigeration circuit 6. Then, the vessel circumference above a flange 3 is covered with a shutoff body 7 as shown in (c). Thereafter, water is filled in the pressure vessel 1, a base 4, and the shutoff body 7, respectively. A coolant is circulated in the coolant pipe 5. After the lapse of a prescribed time, a frozen body 20 in which the outside and inside of the pressure vessel 1 are integrated is formed. The frozen body 20 is vertically and laterally cut into two or more pieces 20a by a wire saw 21. After the cutting work, the ice is thawed by naturally or forcedly raising the temperature of the respective cut pieces 20a, and the resulting water is separately treated, whereby each cut piece 20 is reduced in weight.