A motor control system (100a, 100b, 100c) comprising: a motor; a drive device that applies a voltage to the motor; a computation device that computes a voltage command value indicating the voltage applied to the motor and generates a control signal for controlling the drive device based on the voltage command value; a switch that is connected in series between the computation device and the drive device and turns on and off supplying of the control signal (S pwm) from the computation device to the drive device; an overcurrent detection circuit (7A, 7B) that has a function of turning off the switch when an absolute value of a detection value of a current flowing in the motor exceeds a first threshold value; and a monitoring device that makes a diagnosis for the computation device, wherein the computation device computes the voltage command value so as to cause the absolute value of the detection value of the current flowing in the motor to be equal to or smaller than a second threshold value when a diagnostic result obtained by the monitoring device indicates normality, and computes the voltage command value so as to cause the absolute value of the detection value of the current flowing in the motor to be equal to or smaller than a third threshold value which is smaller than the second threshold value when the diagnostic result obtained by the monitoring device indicates abnormality, wherein one of the following two i) or ii) and additionally the following iii) is fulfilled: i) wherein the monitoring device enables a function of the overcurrent detection circuit when the diagnostic result (R d) indicates abnormality; ii) wherein the function of the overcurrent detection circuit is enabled at all times, wherein the monitoring device sets the first threshold value to a certain value Th1 when the diagnostic result indicates normality and sets the first threshold value to a value Th2 which is smaller than the value Th1 when the diagnostic result indicates abnormality; iii) wherein the motor is a drive motor of a vehicle, and wherein the third threshold value is equal to or smaller than a value corresponding to magnitude of torque at which a brake can stop the vehicle and is equal to or greater than a value corresponding to magnitude of torque at which the vehicle can be driven at a low speed. a motor; a drive device that applies a voltage to the motor; a computation device that computes a voltage command value indicating the voltage applied to the motor and generates a control signal for controlling the drive device based on the voltage command value; a switch that is connected in series between the computation device and the drive device and turns on and off supplying of the control signal (S pwm) from the computation device to the drive device; an overcurrent detection circuit (7A, 7B) that has a function of turning off the switch when an absolute value of a detection value of a current flowing in the motor exceeds a first threshold value; and a monitoring device that makes a diagnosis for the computation device, wherein the computation device computes the voltage command value so as to cause the absolute value of the detection value of the current flowing in the motor to be equal to or smaller than a second threshold value when a diagnostic result obtained by the monitoring device indicates normality, and computes the voltage command value so as to cause the absolute value of the detection value of the current flowing in the motor to be equal to or smaller than a third threshold value which is smaller than the second threshold value when the diagnostic result obtained by the monitoring device indicates abnormality, wherein one of the following two i) or ii) and additionally the following iii) is fulfilled: i) wherein the monitoring device enables a function of the overcurrent detection circuit when the diagnostic result (R d) indicates abnormality; ii) wherein the function of the overcurrent detection circuit is enabled at all times, wherein the monitoring device sets the first threshold value to a certain value Th1 when the diagnostic result indicates normality and sets the first threshold value to a value Th2 which is smaller than the value Th1 when the diagnostic result indicates abnormality; iii) wherein the motor is a drive motor of a vehicle, and wherein the third threshold value is equal to or smaller than a value corresponding to magnitude of torque at which a brake can stop the vehicle and is equal to or greater than a value corresponding to magnitude of torque at which the vehicle can be driven at a low speed. i) wherein the monitoring device enables a function of the overcurrent detection circuit when the diagnostic result (R d) indicates abnormality; ii) wherein the function of the overcurrent detection circuit is enabled at all times, wherein the monitoring device sets the first threshold value to a certain value Th1 when the diagnostic result indicates normality and sets the first threshold value to a value Th2 which is smaller than the value Th1 when the diagnostic result indicates abnormality; iii) wherein the motor is a drive motor of a vehicle, and wherein the third threshold value is equal to or smaller than a value corresponding to magnitude of torque at which a brake can stop the vehicle and is equal to or greater than a value corresponding to magnitude of torque at which the vehicle can be driven at a low speed.