To reduce the skew angle components in a dipole ring magnetic field generating device, a magnetic field generating device 1 is provided in which comprises: a plurality of magnet elements 101 to 124 arranged in a ring shape such that a magnetization direction of the magnet elements undergoes one rotation over half a circumference of the ring, wherein the magnet elements generate a substantially unidirectional magnetic field in a space within the ring; and corrective magnets 201 to 204 arranged on an outer edge portion forming an aperture in a Z-axis direction of the magnetic field generating device, wherein the Z-axis is defined as a central axis of the magnetic field generating device, the Y-axis is defined as a direction perpendicular to the Z-axis and parallel to the unidirectional magnetic field, and the X axis is defined as a direction perpendicular to the Z axis and the Y axis.