To provide a chamber apparatus for gaseous displacement which supplies a gas into a chamber in a short time while suppressing raising of dust with a simple structure, and to provide a method for manufacturing an optical element.

The chamber apparatus for gaseous displacement includes: a chamber 11 whose inside is decompressed by a decompression device, and into which a gas is supplied by a gas supply apparatus; a shielding part 12 which shields and diffuses the gas A1, supplied to the chamber 11, in the chamber 11; and rectification parts 13 and 14 which rectify A3 and A4 the gas A2 diffused by the shielding part 12.