A design assisting apparatus of a steering device arranges a coordinate of a handle position reference point, a coordinate of a first universal joint reference point, a coordinate of a second universal joint reference point, and a coordinate of a steering gear reference point in a three-dimensional space, calculates a reference axis passing through the second universal joint reference point from the first universal joint reference point, calculates a phase angle which is an angle between a straight line from the handle position reference point to the first joint reference point when viewed along the reference axis and a straight line from the second joint reference point to the steering gear reference point when viewed along the reference axis, and determines success or failure of a condition in which the allowable range of the phase angle allowable error is included in the allowable range of the allowable torque variation rate.