PURPOSE: To continuously obtain a soft organic material such as sponge ball for cleaning the inner surfaces of tubes of a tube type heat exchanger quickly and massively at a high accuracy by molding soft organic material susceptible to a elastic deformation as frozen containing water.

CONSTITUTION: A sponge material having holes is made to contain water with a vacuum pump 11 to obtain a soft sponge material 10 containing water. Water is drained with a two-way drain valve 15 and a three-way switch valve 14 is turned to the position of a liquid nitrogen feeder 12, a liquefied nitrogen or the like is used to obtain a frozen sponge material 17 by cooling. Then, it is cut with an electric cutter or the like and spherically molded continuously.

EFFECT: This enables machining in place of the conventional work to save the working time and labor costs.