There is provided an internal-combustion-engine starting apparatus that eliminates the restriction that the portion of the output axle at the axial-direction anti-motor side needs to be narrower than the inner diameter of an inner ring portion and that eliminates the requirement that a member for restricting the output axle from traveling toward the axial-direction anti-motor side is added as an extra component. An internal-combustion-engine starting apparatus is characterized in that the outer helical spline includes an outer ridge portion, in that an inner helical spline includes a both-side opened recess groove portion and a one-side opened recess groove portion in that the outer ridge portion engages with the one-side opened recess groove portion, and in that the axial-direction length of the inner small-diameter portion is the same as or larger than the axial-direction length of the outer ridge portion.