Control device and control method for electric power steering apparatus, and motor module

A control device includes a processor and a storage device storing a program for controlling an operation of the processor. The processor determines whether a vehicle is in a straight-ahead traveling state, based on a vehicle speed detected by a vehicle speed sensor, a steering wheel torque applied to a steering wheel, and a steering wheel angle as a rotation angle of an input shaft. The processor stores the steering wheel angle in the memory when determining that the vehicle is in the straight-ahead traveling state. The processor stores the steering wheel angle in the memory multiple times when determining that the vehicle is in the straight-ahead traveling state. The processor calculates a corrected steering angle amount from a weighted average of the steering wheel angles stored in the memory.