A method of joining a plurality of conductor segments (10a, 10b) each inserted in at least one of a plurality of slots formed in a stator core, each of the plurality of conductor segments (10a, 10b) having a turn portion (10c1, 10c2), straight portions (13a, 13b) and tip ends (111, 112, 113, 114, 115, 116, 117, 118; 151, 152, 153, 154) projecting from a corresponding at least one of the plurality of slots, the method comprising the steps of: (a) arranging the tip ends (111, 112, 113, 114, 115, 116, 117, 118; 151, 152, 153, 154) of the plurality of conductor segments (10a, 10b) such that a plurality of pairs (15a1, 15a2, 15a3, 15a4; 15a10, 15a 11) of the tip ends (111, 112, 113, 114, 115, 116, 117, 118; 151, 152, 153, 154) of the plurality of conductor segments (10a, 10b) are formed, the plurality of tip-end pairs (15al, 15a2, 15a3, 15a4; 15a10, 15a 11) including a first tip-end pair (15a1) and a second tip-end pair (15a2), at least one of first paired conductor segments (10a, 10b) corresponding to the first tip-end pair (15a1) included in the plurality of conductor segments (10a, 10b) and at least one of second paired conductor segments (10a, 10b) corresponding to the second tip-end pair (15a2) included in the plurality of conductor segments (10a, 10b) being electrically connected to each other; (b) preparing a inner ground electrode; (c) preparing a welding electrode; (d) moving the inner ground electrode so as to be in contact with one tip end of the first tip-end pair (15a1) of the first paired conductor segments (10a, 10b); (e) moving the welding electrode so as to be opposite to the first tip-end pair (15a1) of the first paired conductor segments (10a, 10b); (f) establishing electric conduction between the inner ground electrode and the welding electrode via the first tip-end pair of the first paired conductor segments (10a, 10b) so as to weld the first tip-end pair (15a1) of the first paired conductor segments (10a, 10b) based on the electrical conduction therebetween; (g) moving the welding electrode so as to be opposite to the second tip-end pair (15a2) of the second paired conductor segments (10a, 10b) while the inner ground electrode is kept in contact with the tip end of the first tip-end pair (15a1) of the first paired conductor segments (10a, 10b); and (h) establishing electric conduction between the inner ground electrode and the welding electrode via the welded first tip-end pair (15a1) of the first paired conductor segments (10a, 10b) and the second tip-end pair (15a2) of the second paired conductor segments (10a, 10b) so as to weld the second tip-end pair (15a2) of the second paired conductor segments (10a, 10b) based on the electrical conduction therebetween. (a) arranging the tip ends (111, 112, 113, 114, 115, 116, 117, 118; 151, 152, 153, 154) of the plurality of conductor segments (10a, 10b) such that a plurality of pairs (15a1, 15a2, 15a3, 15a4; 15a10, 15a 11) of the tip ends (111, 112, 113, 114, 115, 116, 117, 118; 151, 152, 153, 154) of the plurality of conductor segments (10a, 10b) are formed, the plurality of tip-end pairs (15al, 15a2, 15a3, 15a4; 15a10, 15a 11) including a first tip-end pair (15a1) and a second tip-end pair (15a2), at least one of first paired conductor segments (10a, 10b) corresponding to the first tip-end pair (15a1) included in the plurality of conductor segments (10a, 10b) and at least one of second paired conductor segments (10a, 10b) corresponding to the second tip-end pair (15a2) included in the plurality of conductor segments (10a, 10b) being electrically connected to each other; (b) preparing a inner ground electrode; (c) preparing a welding electrode; (d) moving the inner ground electrode so as to be in contact with one tip end of the first tip-end pair (15a1) of the first paired conductor segments (10a, 10b); (e) moving the welding electrode so as to be opposite to the first tip-end pair (15a1) of the first paired conductor segments (10a, 10b); (f) establishing electric conduction between the inner ground electrode and the welding electrode via the first tip-end pair of the first paired conductor segments (10a, 10b) so as to weld the first tip-end pair (15a1) of the first paired conductor segments (10a, 10b) based on the electrical conduction therebetween; (g) moving the welding electrode so as to be opposite to the second tip-end pair (15a2) of the second paired conductor segments (10a, 10b) while the inner ground electrode is kept in contact with the tip end of the first tip-end pair (15a1) of the first paired conductor segments (10a, 10b); and (h) establishing electric conduction between the inner ground electrode and the welding electrode via the welded first tip-end pair (15a1) of the first paired conductor segments (10a, 10b) and the second tip-end pair (15a2) of the second paired conductor segments (10a, 10b) so as to weld the second tip-end pair (15a2) of the second paired conductor segments (10a, 10b) based on the electrical conduction therebetween.