Abstract: In the apparatus: Y table 43 carries a work W and travels a predetermined distance in direction Y in a reciprocating manner; X table 41 causes the work W to reciprocate in direction X between a first position, in which the work W is loaded onto and unloaded from Y table 43, and a fourth position, in which an induction heating coil 23 is disposed; X table 41 is mounted on a base frame 11; a first reference on Y table 43 positions rows of quenched portions 76a of the work W in desired locations when the work W is loaded onto Y table 43; a second reference on Y table 43 serves as a reference for determining coordinates of Y table 43; a position measuring means 32 in a second position intermediate between the first and the third position measures coordinates of the second reference and of the quenched portions 76a; and, a control means 100 issues signals to control X-Y table 40 together with the heating coil 23 based on the measured coordinates.

Abstract: An induction heating coil for forming a hardened layer in the inner wall of an external cylindrical member to be heated is disclosed. On the inner wall of the conductive induction member, a plurality of recess portions are formed at predetermined spaces circumferentially. The portions of the inner wall of the external cylindrical member to be heated which are opposed to the recess portions can be separately heated, in order collectively to form a plurality of separate partial hardened layers in the inner wall of the external cylindrical member to be heated circumferentially.