A serial printer suitable for use in desk-top calculators or the like. The serial printer has a rotary shaft rotatable together with two type wheels. The power supply to the rotary shaft is made by a motor which operates continuously only in one rotational direction through a first clutch. A second clutch is provided to make a selective power transmission between the motor and the member for actuating the hammer, as well as the member of causing the carrying operation. The states of the first and the second clutches are controlled by a change-over arm which in accordance with the operation instruction given by an operation instruction coil, such that these clutches are alternatively engaged and dis-engaged to make various operations such as printing, column shift, paper feeding and so forth.