Manufacturing method of gear

A manufacturing method of a gear comprising:

• rotating a rod-shaped workpiece around a first axis;
• rotating a tool having a cutting edge on an outer peripheral side around a second axis at a twisted position with respect to the first axis;
• and
• while relatively moving the workpiece and the tool in a direction parallel to the first axis at a speed synchronized with a rotation speed of the workpiece, forming a spiral tooth groove on an outer peripheral surface of the workpiece by bringing the cutting edge of the tool into contact with the outer peripheral surface of the workpiece and removing a material of the workpiece at a contact position by the relative movement between the tool and the workpiece, wherein
• in a plane perpendicular to the first axis, the workpiece is rotated around the first axis and the workpiece and the tool are relatively moved in the direction parallel to the first axis at the speed synchronized with the rotation speed of the workpiece such that a contour line of the cutting edge of the tool is in rolling contact with a target contour line, which is a contour line of the spiral tooth groove to be formed, at a predetermined point of the target contour line or an extension line of the target contour line without slipping, and rotates while sliding with respect to the target contour line or the extension line at a point other than the predetermined point, and
• in the plane perpendicular to the first axis, a diameter of a first circle, which is a circle centered on the first axis and passing through the predetermined point, is 1 time or more and 1.5 times or less a diameter of a second circle which is a tooth tip circle of the gear manufactured from the workpiece centered on the first axis.