According to the present invention, by providing an extremely simple member such as a partition wall having a microscopic hole section, it is possible to reliably reduce the speed of a bullet to within a fixed speed, even a complicated decompression device such as a regulator is not provided. As a result, manufacturing time for the air gun is shortened, it is possible to lower manufacturing cost, and there is the effect of improving the manufacturing efficiency.This is because with an air gun or a magazine for an air gun of the present invention, by having a structure where the opening area of the microscopic hole section of the partition wall is smaller that the gas discharge path opening when the gas discharge path of the discharge valve is open, the gas volume per unit time that flows into the discharge valve chamber from the gas canister side by means of the microscopic holes section is smaller than the gas volume per unit time that flow out from the discharge valve chamber as a result of opening the gas discharge path of the discharge valve, which means that gas speed and gas pressure from the discharge valve chamber to the chamber where a bullet is positioned is lowered. The firing speed of a bullet is thus reduced.