<p>The disclosed invention achieves a proper speed control of a sheet feeding motor for a serial printer that uses an astable power supply with a simple operation irrespective of variations in power supply voltage. The invention provides a method of and an apparatus for controlling the frequency of a sheet feeding pulse motor for a printer in accordance with the power supply voltage during sheet feeding. The apparatus of the invention is composed of a sheet feeding motor controller for use in a printer, the controller controlling a driving signal used to drive a motor in accordance with the level of a printer power supply voltage within the printer, the controller includes a device for detecting a power supply voltage; a first memory device for storing information representing the characteristic voltage restoration curve of the printer power supply; a second memory device for storing information representing the relationship between a rotational speed of the motor and the plurality of voltages making up the characteristic printer power supply restoration curve; a device for estimating a current power supply voltage on the characteristic restoration curve from the information stored in the first memory device; a device for reading a rotational speed from said second memory device corresponding to the current power supply voltage estimated by said estimating means; and a device for changing the speed of the motor in accordance with the read rotational speed.</p>
