A method for manufacturing a spline telescopic shaft (5; 5C), the method comprising the steps of: preparing a first manufacturing intermediate member (555; 57C) which is an intermediate member (555; 555C) for manufacturing an inner shaft having a core tooth portion formed on its outer periphery or an intermediate member (57; 57C) for manufacturing a cylindrical outer shaft having a core tooth portion formed on its inner periphery; preparing a second manufacturing intermediate member (57; 555C) which is the other (57; 555C) of the intermediate member (57; 57C) for manufacturing the cylindrical outer shaft having the core tooth portion formed on its inner periphery or the intermediate member (555; 555C) for manufacturing the inner shaft having the core tooth portion formed on its outer periphery; providing a first resin coating on the surface of the core tooth portion of the first manufacturing intermediate member; fitting the first manufacturing intermediate member and the second manufacturing intermediate member by a press fitting; and sliding the first manufacturing intermediate member and the second manufacturing intermediate member which are pressed coupled with each other by forcibly sliding in an axial direction of the first and the second manufacturing intermediate members, characterized in that in the sliding step, frictional heat is applied to the first resin coating on the first manufacturing intermediate member so that a part of the first resin coating (59; 59C) is transferred to the surface (48a; 42a) of the core tooth portion (48; 42) in the second manufacturing intermediate member (57; 555C), to form a second resin coating (46; 46B; 46C) on the surface (48a; 42a) of the core tooth portion (48; 42) in the second manufacturing intermediate member (57; 555C). preparing a first manufacturing intermediate member (555; 57C) which is an intermediate member (555; 555C) for manufacturing an inner shaft having a core tooth portion formed on its outer periphery or an intermediate member (57; 57C) for manufacturing a cylindrical outer shaft having a core tooth portion formed on its inner periphery; preparing a second manufacturing intermediate member (57; 555C) which is the other (57; 555C) of the intermediate member (57; 57C) for manufacturing the cylindrical outer shaft having the core tooth portion formed on its inner periphery or the intermediate member (555; 555C) for manufacturing the inner shaft having the core tooth portion formed on its outer periphery; providing a first resin coating on the surface of the core tooth portion of the first manufacturing intermediate member; fitting the first manufacturing intermediate member and the second manufacturing intermediate member by a press fitting; and sliding the first manufacturing intermediate member and the second manufacturing intermediate member which are pressed coupled with each other by forcibly sliding in an axial direction of the first and the second manufacturing intermediate members, characterized in that in the sliding step, frictional heat is applied to the first resin coating on the first manufacturing intermediate member so that a part of the first resin coating (59; 59C) is transferred to the surface (48a; 42a) of the core tooth portion (48; 42) in the second manufacturing intermediate member (57; 555C), to form a second resin coating (46; 46B; 46C) on the surface (48a; 42a) of the core tooth portion (48; 42) in the second manufacturing intermediate member (57; 555C).