A speed control device for an electric turbocharger arranged to deliver turbocharged-air to an internal combustion engine by a motor driving the turbocharger, the speed control device comprising: a temperature sensor arranged to detect a temperature of the motor or a temperature of an other part which is correlated with the temperature of the motor; and a speed limitation device arranged to limit the speed of the motor when the temperature level detected by the temperature sensor exceeds a limit control start temperature, the speed control device characterized in that: the speed limitation device comprises: a limit control start temperature correction device arranged to decrease the limit control start temperature in a case that the increase rate of the temperature detected by the temperature sensor exceeds a threshold; and a speed limitation setting device arranged to set a speed limit level based on a temperature difference between the limit control start temperature and the detected temperature, as well as based on an increase rate of the detected temperature, after the detected temperature exceeds the limit control start temperature, wherein the speed of the motor is limited to the speed limit level set by the speed limitation setting device. a temperature sensor arranged to detect a temperature of the motor or a temperature of an other part which is correlated with the temperature of the motor; and a speed limitation device arranged to limit the speed of the motor when the temperature level detected by the temperature sensor exceeds a limit control start temperature, the speed control device characterized in that: the speed limitation device comprises: a limit control start temperature correction device arranged to decrease the limit control start temperature in a case that the increase rate of the temperature detected by the temperature sensor exceeds a threshold; and a speed limitation setting device arranged to set a speed limit level based on a temperature difference between the limit control start temperature and the detected temperature, as well as based on an increase rate of the detected temperature, after the detected temperature exceeds the limit control start temperature, wherein the speed of the motor is limited to the speed limit level set by the speed limitation setting device. the speed limitation device comprises: a limit control start temperature correction device arranged to decrease the limit control start temperature in a case that the increase rate of the temperature detected by the temperature sensor exceeds a threshold; and a speed limitation setting device arranged to set a speed limit level based on a temperature difference between the limit control start temperature and the detected temperature, as well as based on an increase rate of the detected temperature, after the detected temperature exceeds the limit control start temperature, wherein the speed of the motor is limited to the speed limit level set by the speed limitation setting device. a limit control start temperature correction device arranged to decrease the limit control start temperature in a case that the increase rate of the temperature detected by the temperature sensor exceeds a threshold; and a speed limitation setting device arranged to set a speed limit level based on a temperature difference between the limit control start temperature and the detected temperature, as well as based on an increase rate of the detected temperature, after the detected temperature exceeds the limit control start temperature, wherein the speed of the motor is limited to the speed limit level set by the speed limitation setting device.