In order to examine the electronic structure of amorphous Fe80B20-xMx (M = P, C, Si, Ge), the hyperfine field and the isomer shift of these alloys are obtained and analyzed. The number of the electrons transferred from metalloid to the 3d band of Fe is estimated on the basis of the "rigid band-donor" model. It is shown that the 4s electrons of iron take part in the charge transfer process. A possible resolution of the contradiction between the variation of magnetic moment and the counter charge transfer to the "rigid band-donor" model is given.