A heat treatment method is capable of molding, by mobile quenching of induction quenching, an outer joint member of a tripod type constant velocity universal joint having excellent strength without forming hardened layers in larger radially-inner portions. Mobile quenching is performed in such a manner that a high-frequency induction heating coil is moved in an axial direction relative to an outer joint member, and thus hardened layers are formed on the roller guide surfaces. Magnetic field line cut-out bodies for cutting out generated magnetic field lines are arranged on the high-frequency induction heating coil. The larger radially-inner portions become an unquenched portion by cutting out the magnetic field lines with the magnetic field line cut-out bodies.