We report a systematic high-resolution angle-resolved photoemission spectroscopy on high-T c superconductors Bi 2 Sr 2 Ca nÿ1 Cu n O 2n4 (n 1-3) to study the origin of many-body interactions responsible for superconductivity. For n 2 and 3, a sudden change in the energy dispersion, so called "kink", becomes pronounced on approaching (; 0) in the superconducting state, while a kink appears only around the nodal direction in the normal state. For n 1, the kink shows no significant temperature

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... ndence even across T c . This could suggest that the coupling of electrons with Q ; magnetic mode is dominant in the superconducting state for multilayered cuprates, while the interactions at the normal state and that of single-layered cuprates have a different origin.