Disclosed is a cartridge for an air gun that facilitates the loading of a bullet into the cartridge. The cartridge includes cylindrical unitary cartridges into which bullets are to be inserted, a cartridge assembly in which the unitary cartridges are coupled to each other and continuously disposed between both ends to form a strip shape, and a magazine case that houses the cartridge assembly. The cartridge assembly is transported by a cartridge transport unit. Further, the unitary cartridges each include two cylindrical parts. The cylindrical parts of neighboring unitary cartridges are sequentially fit-coupled to each other in order to form the cartridge assembly.