A printer includes a platen roller, a motor configured to rotate the platen roller, and a frame configured to rotatably support the platen roller, the motor being mounted to the frame, wherein the motor has a shaft and a face that is in contact with the frame, and the face has a flange at a periphery thereof and a boss around the shaft, wherein the frame has a U-letter-shape opening into which the boss of the motor is insertable in a direction perpendicular to an axis of the shaft, and also has a fitting part in which the flange of the motor is engaged, and wherein the motor is fixedly positioned by the boss being inserted into the U-letter-shape opening of the frame and by the flange being engaged in the fitting part.