A method for manufacturing a gear includes rotating a workpiece around a first axis, and rotating a plurality of cutting blades arranged annularly around a second axis skew to the first axis around the second axis. The method further includes, while causing the workpiece and the cutting blades to perform relative movement in a direction parallel to the first axis at a speed synchronized with a rotational speed of the workpiece, forming a helical tooth groove in an outer peripheral surface of the workpiece by the cutting blades. In a cross section perpendicular to the first axis, a diameter of a rolling circle in which an outline of the cutting blades and a target online of the gear make rolling contact with each other is larger than a diameter of a tooth depth center circle.