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 = α, and scanning in an X' direction perpendicular to the longitudinal direction of the measuring part (21) is repeated while changing an angle θ 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', θ) obtained by repetitions of the scanning are Fourier transformed so as to obtain g(kx', θ) (where kx' is a wavenumber in the X' direction). Then, g(kx', θ) is substituted into a predetermined two-dimensional potential obtaining equation so as to obtain φ(x, y, α) 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.
