A valence fluctuating phenomenon, which is one of the most interesting subjects in strongly correlated electron systems, has been studied theoretically in EuNi2(Si0.18Ge0.82)(2), in which the field-induced valence transition from a nonmagnetic Eu3+ state (4f(6)) to a magnetic Eu2+ state (4f(7)($) under bar (1)) was observed at around 40 Tesla by means of X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at Eu L-edges. Here, c denotes a hole in a conduction band. Both XAS and XMCD in fields exhibit two peaks corresponding to the two valence states, although one of them is nonmagnetic. In this paper, we propose a model to explain the field-induced valence transition, in which the hybridization between the 4f(6) state and the 4f(7)(c) under bar (1) state plays an essential role. Comparing XAS and XMCD calculated with experimental data, we fi nd that XAS and XMCD provide us with detailed microscopic information on the mixed valence state through the polarized 5d electrons. Finally, we demonstrate how effective XAS and XMCD are for studying such mixed valence phenomena.