Summary form only given. The paper deals with the problem of the electromagnetic field analysis in incommensurable regions. These are cases when there is a need for detailed field calculation in a small region, which is a part of larger one. Solving the problem by the finite element method, this would lead either to usage of elements of disproportionate dimensions or to a huge number of elements. The problem is solved by an iteration procedure. The forward step involves electromagnetic field analysis in the entire region and successive investigation of the small region only. The latter is carried out by applying the boundary values obtained from the analysis of the entire region. The back step includes taking into account the influence of the field redistribution in the small region on the field in the entire domain. The procedure terminates after reaching the desired accuracy. The proposed approach is illustrated by an example of an electromagnetic device. The computed results are compared to experimental ones. The error due to the usage of disproportionate elements in the small region is also estimated.