A heat-treating furnace with a magnetic field comprising (a) a magnetic field-generating means constituted by an outer, ring-shaped, permanent magnet assembly comprising a plurality of permanent magnet segments combined with their magnetization directions oriented such that a magnetic flux flows in a diameter direction, and an inner, ring-shaped, permanent magnet assembly disposed inside the outer, ring-shaped, permanent magnet assembly and comprising a plurality of permanent magnet segments combined with their magnetization directions oriented such that a magnetic flux flows in a diameter direction; and (b) a heat treatment means disposed in a center hole of the inner, ring-shaped, permanent magnet assembly and comprising a cooling means, a heating means, and a heat-treating container containing heat-treating holder for holding a plurality of articles to be heat-treated in this order from outside, wherein an axial center of a magnetic field generated by the inner and outer ring-shaped, permanent magnet assemblies is substantially identical with an axial center of an article assembly in the heat-treating container.