PURPOSE: To enable to perform extremely simplified quenching, in the titled apparatus for surface quenching the small-diameter and shoulder parts of a shaft body having at least a plurality of small and large diameter parts while rotating said shaft body about its axis, by organizing a heating coil and a cooler into a specified state.

CONSTITUTION: The inner wall of a heating coil C for surface quenching a shaft body W comprises a semicircular arc Va having a center Oa capable of facing to the periphery of a small-diameter part Wa with a predetermined gap, and notched arcs Vb slightly larger than the periphery of a large diameter part Wb, having a center Ob continuous to both sides of said arc Va. Coolers Q maintaining the width in the manner that a space surrounded with their inner walls is similar to or larger than the diameter of the arc Vb and length nearly equal to the sum of the diameter of the arc Vb and the radius of the arc Va are symmetrically provided in close vicinity to both sides of the coil C, to constitute the quenching apparatus in an integrated structure. During quenching, it is displaced along the axial direction of the center at the original 1 from the position of the coil C, and the shaft body W is rotated while supporting its center and sequentially and relatively moved along positions 2W8 in the drawing. Said shaft body W is heated by applying an electric current to the coil C, and a cooling fluid is sprayed inward obliquely backwards along the moving direction of only the cooler Q located at the following side.