In order to clarify many-body interactions in ferromagnetic iron, we performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on a Fe(110) single crystal. We quantitatively analyzed the ARPES line shapes for a majority-spin band crossing the Fermi level (EF). The observed group velocity was reduced with respect to the band-structure calculation by a factor of 1/2.7, giving a coupling parameter due to the electron-electron interaction of λee=1.7±0.1. This suggests a strong electron correlation in Fe 3d, which is consistent with recent high-resolution ARPES results. The real and imaginary parts of the self-energy have been experimentally evaluated near EF. The coupling parameter of the electron-phonon interaction was estimated to be λep=0.16±0.02, which is 1/10 of λee. The effective-mass enhancement with respect to the band mass m∗/mb∼1+λee+λep∼3 was, therefore, mainly caused by electron correlation.