Semianalytic method for calculation of coupling impedance produced by an inhomogeneity of vacuum chamber is developed. The inhomogeneity can be shaped quite generally but it has to be of the same (axial or flat) symmetry as the vacuum chamber. Substituting solutions of Maxwell equations for electromagnetic fields which contain an unknown function into wall boundary conditions leads to the integral equation. Its solution in some point gives the coupling impedance. To illustrate method potentialities the low-frequency longitudinal impedance of some chamber insertions having various shapes is numerically investigated. An example of resonances calculation is also presented. Moreover interaction of a few insertions is considered. 11 refs.; 8 figs.