PURPOSE: To obtain efficiently a hollow sphere whose diameter is small and whose wall is thin, by lowering the temperature of a melted resin a little, stirring it under reduced pressure, and while expanding the melted resin through a gas blowing pipe and an orifice, cutting the melted resin.

CONSTITUTION: The temperature of a thermoplasic resin in a tank 9 is elevated by a heater 8 to a temperature where it will not boil, and is lowered to an optimum temperature. The inside of the tank is kept vacuum, the resin is stirred, is allowed to depend in the shape of a tube, air is blown into the tube to expand it into a balloon, and while it is expanded at an orifice it is cut into a hollow sphere, which is cooled to be solidified. Such hollow spheres are collected in a hopper 22.