There is provided a magnetic field generator 10 which is capable of generating a uniform magnetic field of a desired intensity easily and stably without increasing running cost. The magnetic field generator 10 includes a pair of plate yokes 12a, 12b. The plate yokes 12a, 12b have opposed surfaces provided with magnetic pole 14a, 14b respectively. The magnetic pole 14a includes a permanent magnet group 16a whereas the magnetic pole 14b includes a permanent magnet group 16b. Each of the permanent magnet groups 16a, 16b is formed substantially in a disc like shape, as an integral body made of a plurality of permanent magnets 20 and a plurality of heat conducting members 22. Tubular heaters 34, buried in the plate yokes 12a, 12b, generate heat, which is conducted via the plate yokes 12a, 12b to each permanent magnet 20 and each heat conducting member 22 which constitute the permanent magnet groups 16a, 16b.