A heat treatment method for forming hardened layers in roller guide surfaces of an outer joint member, comprising: performing mobile quenching in such a manner that a high-frequency induction heating coil is moved in an axial direction relative to the outer joint member comprising track grooves which are formed at three positions of an inner periphery of the outer joint member, and each of which comprises: the roller guide surfaces facing to each other in a circumferential direction of the outer joint member; and a larger radially-inner portion provided between both of the roller guide surfaces, wherein, correspondingly to the relative movement of the high-frequency induction heating coil, radially-inner surfaces of the outer joint member are subsequently heated, and following the heating, the heated surfaces are rapidly cooled with a cooling fluid to form the hardened layers, characterized by providing heating-suppressing portions for the larger radially-inner portions in positions of the high-frequency induction heating coil, the positions being respectively opposed to the larger radially-inner portions; and setting a range corresponding to a boot mounting portion in at least a center portion in the circumferential direction in each of the larger radially-inner portions of the outer joint member to be an unquenched portion by the heating-suppressing portions, wherein: the heating-suppressing portions for the larger radially-inner portions comprise magnetic field line cut-out bodies for cutting out magnetic field lines generated through the high-frequency induction heating coil; and the magnetic field line cut-out bodies comprise ferromagnetic cores fitted into portions of the high-frequency induction heating coil, at which the ferromagnetic cores come close to the larger radially-inner portions, respectively. performing mobile quenching in such a manner that a high-frequency induction heating coil is moved in an axial direction relative to the outer joint member comprising track grooves which are formed at three positions of an inner periphery of the outer joint member, and each of which comprises: the roller guide surfaces facing to each other in a circumferential direction of the outer joint member; and a larger radially-inner portion provided between both of the roller guide surfaces, the roller guide surfaces facing to each other in a circumferential direction of the outer joint member; and a larger radially-inner portion provided between both of the roller guide surfaces, wherein, correspondingly to the relative movement of the high-frequency induction heating coil, radially-inner surfaces of the outer joint member are subsequently heated, and following the heating, the heated surfaces are rapidly cooled with a cooling fluid to form the hardened layers, characterized by providing heating-suppressing portions for the larger radially-inner portions in positions of the high-frequency induction heating coil, the positions being respectively opposed to the larger radially-inner portions; and setting a range corresponding to a boot mounting portion in at least a center portion in the circumferential direction in each of the larger radially-inner portions of the outer joint member to be an unquenched portion by the heating-suppressing portions, wherein: the heating-suppressing portions for the larger radially-inner portions comprise magnetic field line cut-out bodies for cutting out magnetic field lines generated through the high-frequency induction heating coil; and the magnetic field line cut-out bodies comprise ferromagnetic cores fitted into portions of the high-frequency induction heating coil, at which the ferromagnetic cores come close to the larger radially-inner portions, respectively. the heating-suppressing portions for the larger radially-inner portions comprise magnetic field line cut-out bodies for cutting out magnetic field lines generated through the high-frequency induction heating coil; and the magnetic field line cut-out bodies comprise ferromagnetic cores fitted into portions of the high-frequency induction heating coil, at which the ferromagnetic cores come close to the larger radially-inner portions, respectively.