Effects of steel-skeletons on the geomagnetic distribution in building have been studied through the simulation and measurement of geomagnetic distribution at floor surface. Geomagnetic distribution was simulated by the finite element method, and the vertical component Z of geomagnetic field on the floor surface was measured with the fluxgate-type magnetometer. Horizontal steel-skeletons have a little effect on the Z distribution, but vertical skeletons disturb severely the Z distribution and result in the localized geomagnetic disturbance. This disturbance becomes weakened by the bypassing soft-magnetic plate and/or floor.