Method for manufacturing gear

A method for manufacturing a gear, the method comprising:

• setting a function f(x) for forming a predetermined tooth profile in a gear, the function f(x) being defined so that:
• a surface shape of the tooth profile from a tooth root to a tooth tip has a vertex;
• a difference between a radius of curvature of the surface shape of the tooth profile at the tooth root and a radius of an arc or a radius of curvature of a parabola at the tooth root is within a predetermined value, the radius of the arc or the radius of curvature of the parabola at the tooth root being in contact with the vertex;
• a difference between a radius of curvature of the surface shape of the tooth profile at the tooth tip and the radius of the arc or a radius of curvature of the parabola at the tooth tip is equal to or greater than a predetermined value;
• and
• the radius of curvature of the surface shape of the tooth profile at the tooth tip becomes smaller than the radius of the arc or the radius of curvature of the parabola at the tooth tip;
• and
• forming the tooth root and the tooth tip by using the function f(x).