Abstract: A rotation speed control circuit is designed to control the rotational speed of a motor at a constant speed, despite variations in both the load and the power supply. A motor (100') and a resistor (R) are connected to a power supply terminal, respectively. A control circuit (200') receives an operation voltage from the resistor R and supplies an output to the other end of the motor (100'). Within the control circuit (200'), the operation voltage is supplied to one end of a comparator (10) through a constant voltage generator (9), and the output is supplied to the other end of the comparator (10) through a resistor (R.sub.11). A output circuit (11) supplies currents both to the motor (100') and to the resistor (R), respectively, in response to the output of the comparator (10).