To assure a stable stage in a die space and to obtain optical blanks having high volume accuracy by dropping the blanks in a fluid state by the same amount as the volume of optical parts after press forming from a prescribed opening and press forming their massive member between the two dies for the blanks of flat planar die surfaces, thereby forming the blanks approximately in a disk shape.

The volume of the massive members 10 is regulated to a desired value by properly setting the temperature and viscosity of optical material, and the shape, diameter and extrusion method, or the like, of a nozzle 11. A plurality of the massive members 10 are arranged between the upper die 12 for the blanks and the lower die 13 for the blanks. The massive members are heated by heating up to the transition point of the optical material. The massive members 10 are soften to have plasticity. The massive members 10 are compressed between the upper die 12 for the blanks and the lower die 13 for the blanks and are press formed to the optical blank 14 of the approximately disk shape. The optical blanks 14 for forming are slowly cooled and are taken out by rising the upper die 10 for the blanks by a pneumatic mechanism, or the like.