To form spheres with a flexible plastic pipe material in such a way as to continuously form spheres for an impact absorber having a specified shape and sealed with air under a specified rising internal pressure from the beginning of the formation of the spheres.

The method of forming spheres continuously comprises forming sealed space portions in a flexible plastic pipe material by occluding the pipe material at constant intervals, applying a parallel pressure to parts of the sealed space portions at a specified distance from the occluded portion so as to transfer the sealed air in the pressurized portions to the remainder of the sealed space portions and thereby form expanded pipe portions expanded because the air pressure in the remaining space portions rises, and carrying out compression and electrothermal adhesion while sandwiching the expanded pipe portions at their middle positions in order to continuously form spheres for an impact absorber of a specified shape and a specified internal air pressure.