In a microcomputer, a signal processing device computes a control signal, such as an accelerator position, a throttle position, based on a sensor output signal, such as an output signal of an accelerator position sensor, an output signal of a throttle position sensor. A torque control device executes a torque control operation to coincide an actual torque with a requested torque based on the control signal. Furthermore, a torque monitor device determines whether a torque increase abnormality exists based on the control signal. A signal abnormality diagnosis device determines whether an operational abnormality of the signal processing device exists based on a relationship between the sensor output signal and the control signal. A monitor IC monitors operational states of the torque monitor device and of the signal abnormality diagnosis device and determines whether an operational abnormality of the torque monitor device or of the signal abnormality diagnosis device exists.