Electric power steering apparatus

An electric power steering apparatus, comprising:

• an electric motor for producing a steering assist force;
• and
• a speed reduction mechanism for decelerating the rotation of an output shaft in the electric motor, the speed reduction mechanism comprising
• a driving gear connected to the output shaft in the electric motor and
• a driven gear meshed with the driving gear,
• said driving gear and said driven gear comprising a first gear and a second gear;
• the first gear comprising a first tooth section and having a first pitch circle and the second gear respectively comprising a second tooth section and having a second pitch circle,
• the first tooth section formed of a material having a relatively low hardness, and the second tooth section formed of a material having a relatively high hardness,
• a flank of the first tooth section formed shifted an increment along a circumference of the first pitch circle such that a thickness of the first tooth section along the circumference of the first pitch circle is larger than a reference thickness of the first tooth section along the circumference of the first pitch circle in a case where the first tooth section is not shifted, and
• a flank of the second tooth section formed shifted a decrement along a circumference of the second pitch circle such that a thickness of the second tooth section along the circumference of the second pitch circle is smaller than a reference thickness along the circumference of the second pitch circle of the second tooth section in a case where the second tooth section is not shifted.