A magnetic field measuring method includes: a first radial-magnetic-field measuring using a magnetic field measuring element placed at an offset position apart from the coil axis, to thereby measure, at the offset position, first radial magnetic fields along an offset axis parallel to the coil axis; a second radial-magnetic-field measuring using the magnetic field measuring element after being rotated by a set angle, to thereby measure, at the offset position, second radial magnetic fields along the offset axis; and a center-position determining the inter-coil center position, based on a first radial-magnetic-field characteristic that is a characteristic in a direction of the offset axis of the first radial magnetic fields, and a second radial-magnetic-field characteristic that is a characteristic in the direction of the offset axis of the second radial magnetic fields.