Three-dimensional modelling methods using the difference method and finite element method are applied to the simulations respectively of the surface electromagnetic method, borehole electromagnetic method, and airborne electromagnetic method, and they are compared with each other in point of accuracy and practicality. The object of calculation in this study is a 3-D model which is a semi-finite medium 100 ohm/m in resistivity that contains a rectangular parallelopiped 1 ohm/m in resistivity. A vertical magnetic dipole is installed on the surface in the surface electromagnetic method, providing a vertical magnetic field on the surface. In the borehole electromagnetic method, a vertical magnetic dipole is placed in a borehole and the resultant vertical magnetic field is measured at a station in another borehole. In the airborne electromagnetic method, the flight level is 20m high and the distance between the source and the receiving point is 10m. The results of calculation all agree well with the results of calculation previously made known. When the difference method and finite element method are compared, it is found that the finite element method requires calculation time and memory capacity two to three times more than the difference method. 5 refs., 9 figs.