A steel gear 1 includes a generally cylindrical outer
peripheral ring portion 2, on an outer
peripheral surface 20a of which a toothed shape 10 is formed, and a
flange portion 3 provided to extend radially inward from an inner
peripheral surface 20b of the outer peripheral ring portion 2. The outer peripheral ring portion 2 includes a first projecting portion 21 that projects toward one side in the axial direction with respect to a
coupling position at which the first projecting portion 21 is coupled to the
flange portion 3, and a second projecting portion 22 that projects toward the other side in the axial direction with respect to a
coupling position at which the second projecting portion 22 is coupled to the
flange portion 3. The
axial length of the first projecting portion 21 is longer than the
axial length of the second projecting portion 22. The outer peripheral ring portion 2 includes a carburized layer 4 formed in a
surface layer of the toothed shape 10, and a thermal history layer 5 formed in a region including the carburized layer 4 and at a depth, in the inward direction from the outer peripheral surface 20a, larger than the depth of the carburized layer 4, the thermal history layer 5 having a history of being heated through high-frequency
induction heating until becoming
austenite. The depth T of the thermal history layer 5 in the inward direction from a tooth bottom 104 of the toothed shape 10 is larger at the second projecting portion 22 than at the first projecting portion 21.