An optical stereolithographic apparatus performs optical stereolithography
by preparing a mask on a light-transmissible member (31) on the basis of
data for one layer with respect to optical stereolithography, exposing an
unhardened resin layer (96) of photohardenable resin to light through the
mask, and repeating an exposure operation. The optical stereolithographic
apparatus has an optical system in which the light-transmissible member
(31) and the unhardened resin layer (96) are spaced from each other at a
predetermined distance, and the unhardened resin layer (96) of the
photohardenable resin is subjected to a projection exposure through the
mask.