When, in devices of various types, a plurality of cartridges 3 and 5 are inserted into prescribed positions of a main device body with a prescribed sequence and a prescribed insertion path formed with guides 16 and 17, the cartridge 5 that is next to be inserted into the main device body 1 is inserted into its prescribed position in main device body 1 by guidance or accompanied by guidance from a guide section 51 provided on cartridge 3 that is previously inserted into its prescribed position in main device body 1. By means of this construction, it is made easy for the operator to notice incorrect insertion where there are a plurality of cartridges and correct cartridge insertion is facilitated.