A credit card printing machine has a carriage with a platen movable over a printing bed on which a credit card and a copy sheet or pad of copy sheets, are placed. A printing plate associated with the credit organization which issued the respective credit card, is detachably attached to a seat plate, and can be exchanged so that the used printing plate and credit card are always associated with the same credit organization. The printing plate prints information regarding the name and code number of the store or dealer making the credit sale in the respective credit organization. This information, together with customer information from the credit card, are both imprinted on the used copy sheet. The attachment of the printing plate is effected by pins and a clamping spring so that no tool is required for exchanging printing plates to conform to the credit organization of a respective used credit card. Other printing plates, associated with other credit organizations, are stored in a compartment of the housing of the printing machine.