In a magnetic field obtaining apparatus, a measuring part (21) that is sufficiently longer than the width of an area to be measured is disposed on a measurement plane that satisfies z = ±, and scanning in an X' direction perpendicular to the longitudinal direction of the measuring part (21) is repeated while changing an angle ¸ formed by a predetermined reference direction on the measurement plane and the longitudinal direction of the measuring part (21) to a plurality of angles. Assuming that x' is a coordinate parameter in the X' direction, measured values f(x', ¸) obtained by repetitions of the scanning are Fourier transformed so as to obtain g(k x' , ¸) (where k x' is a wavenumber in the X' direction). Then, g(k x' , ¸) is substituted into a predetermined two-dimensional potential obtaining equation so as to obtain Æ (x, y, ±) that indicates a two-dimensional potential on the measurement plane. Accordingly, it is possible to perform high-resolution two-dimensional potential measurement as a result of using the measuring part (21) that is sufficiently larger than the width of an area to be measured.
