1. A three-dimensional field obtaining apparatus for obtaining φ(x, y, z), wherein x, y, z show coordinate parameters in a rectangular coordinate system defined by X, Y, Z directions which are orthogonal to one another, or obtaining a function derived by differentiating φ(x, y, z) with respect to z one time or more, φ(x, y, z) being a field function showing a three-dimensional scalar field which is formed at least at a circumference or inside of an object due to the existence of said object and satisfies the Laplace equation, said three-dimensional field obtaining apparatus comprising: a measured value group obtaining part for obtaining a distribution of measured values of one type in a measurement plane as a two-dimensional first measured value group and obtaining a distribution of measured values of another type in said measurement plane as a two-dimensional second measured value group, said measurement plane being set outside or inside an object and satisfying z=0, said distribution of measured values of one type coming from said three-dimensional scalar field, said distribution of measured values of another type coming from said three-dimensional scalar field; and an operation part for obtaining φ z (q) (x, y, 0) and φ z (p) (x, y, 0) which are q times differential and p times differential of φ(x, y, z) in said measurement plane with respect to z, wherein p, q are integers which are equal to or larger than 0 and wherein one of the integers p and q is odd and the other is even, on the basis of said first measured value group and said second measured value group, and calculating φ z (q) (k x , k y ) and φ z (p) (k x , k y ) by Fourier transforming φ z (q) (x, y, 0) and φ z (p) (x, y, 0), respectively, wherein k x , k y are wavenumbers in the X direction and the Y direction, and furthermore calculating φ z (q) (x, y, z) by deriving a Fourier transformed function of φ z (q) (x, y, z) from φ z (q) (k x , k y ) and φ z (p) (k x , k y ).