There is provided a tool for efficiently cutting a face gear to be meshed with a helical gear. When a circular tooth thickness of a tooth tip of a cutting edge portion is represented as S.sub.atSC, a circular tooth thickness on a virtual outside diameter of a tooth profile of the helical gear in a cross-sectional view perpendicular to an axis is represented as S.sub.at, a helix angle on the virtual outside diameter of the tooth profile of the helical gear in a cross-sectional view by a plane perpendicular to the axis is represented as .sub.a, and a face width of the cutting edge portion is represented as b.sub.sc, $b_{\mathrm{SC}}\frac{s_{\mathrm{at}}-s_{\mathrm{atSC}}}{\tan {}_a}$
is satisfied.