In a printer, a sheet feeder includes a motor which is used for a plurality of mechanisms in common so as to make the printer lighter in weight and more compact in size. The sheet feeder can vary the feeding amount of the sheet in response to the printing operation. The sheet feeder also permits the manual operation of a sheet feed roller shaft by disconnecting power from a motor via a power switching mechanism. The power switching mechanism includes a clutch mechanism which has a gear for transmitting the power of the motor, and a clutch wheel. The clutch mechanism is used when feeding the sheet by the operation of the motor. The sheet feeding amount is varied by the operation of a partial gear which comes into contact selectively with a first or second feed cam. These feed cams have projections having different heights.