A magnetic field generator comprising a magnetic circuit of an open magnetic path in which a uniform magnetic field can be generated with a simpler structure. A nuclear magnetic resonance device equipped with this magnetic field generator is also provided. The magnetic field generator of an open magnetic path type comprises a first permanent magnet and a second permanent magnet arranged sequentially in a reference direction at a predetermined interval while directing the direction of magnetization in the reference direction, and a third permanent magnet and a fourth permanent magnet arranged sequentially between the first permanent magnet and the second permanent magnet along the reference direction while touching each other or spaced apart a predetermined interval. Direction of magnetization of the third permanent magnet has a first component parallel with the reference direction and a second component intersecting a first direction perpendicularly and directed toward the region side. Direction of magnetization of the fourth permanent magnet has a first component and an inverted second component reverse to the direction of the second component and having a magnitude identical to that of the second component.