An electric power steering controller comprising: a main microcomputer including: a controller which outputs motor drive signals to a drive circuit based on first and second torque signals (Tmain, Tsub), the drive circuit being adapted to drive a motor that generates assistive torque, the first and second torque signals (Tmain, Tsub) being output from at least one torque sensor (2, 2') used to detect steering force; and a torque sensor abnormality detector which detects an abnormality of the torque sensor (2, 2') based on the first and second torque signals (Tmain, Tsub); wherein the electric power steering controller is characterized by further comprising an external device connected to the main microcomputer, the external device including an excessive torque detector which detects a torque that is larger than a first threshold value using either one of the first and second torque signals (Tmain, Tsub) and which outputs a motor stop signal when the used signal indicates that the torque is larger than the first threshold value; wherein the external device further includes an anomalous current detector for detecting anomalous current using either one of the first and second torque signals (Tmain, Tsub) and for outputting a motor stop signal when a current that flows through the motor exceeds a given current value with the used signal being close to zero, wherein the external device further includes a rack-end protection detector for detecting activation of a rack-end protection when either one of the first and second torque signals (Tmain, Tsub) indicate that a torque is larger than the first threshold value and the amount of a decrease in the current flowing through the motor within a given time frame is larger than a given second threshold value, and wherein the operation of the motor is continued when the rack-end protection detector has detected the activation of the rack-end protection, regardless of whether the anomalous current detector has detected an anomalous current or not. a main microcomputer including: a controller which outputs motor drive signals to a drive circuit based on first and second torque signals (Tmain, Tsub), the drive circuit being adapted to drive a motor that generates assistive torque, the first and second torque signals (Tmain, Tsub) being output from at least one torque sensor (2, 2') used to detect steering force; and a torque sensor abnormality detector which detects an abnormality of the torque sensor (2, 2') based on the first and second torque signals (Tmain, Tsub); wherein the electric power steering controller is characterized by further comprising a controller which outputs motor drive signals to a drive circuit based on first and second torque signals (Tmain, Tsub), the drive circuit being adapted to drive a motor that generates assistive torque, the first and second torque signals (Tmain, Tsub) being output from at least one torque sensor (2, 2') used to detect steering force; and a torque sensor abnormality detector which detects an abnormality of the torque sensor (2, 2') based on the first and second torque signals (Tmain, Tsub); wherein the electric power steering controller is characterized by further comprising an external device connected to the main microcomputer, the external device including an excessive torque detector which detects a torque that is larger than a first threshold value using either one of the first and second torque signals (Tmain, Tsub) and which outputs a motor stop signal when the used signal indicates that the torque is larger than the first threshold value; wherein the external device further includes an anomalous current detector for detecting anomalous current using either one of the first and second torque signals (Tmain, Tsub) and for outputting a motor stop signal when a current that flows through the motor exceeds a given current value with the used signal being close to zero, wherein the external device further includes a rack-end protection detector for detecting activation of a rack-end protection when either one of the first and second torque signals (Tmain, Tsub) indicate that a torque is larger than the first threshold value and the amount of a decrease in the current flowing through the motor within a given time frame is larger than a given second threshold value, and wherein the operation of the motor is continued when the rack-end protection detector has detected the activation of the rack-end protection, regardless of whether the anomalous current detector has detected an anomalous current or not.