A magnetic field generator (G1) for a magnetocaloric thermal device which comprises first (SM11) and second (SM21) identical magnetizing structures mounted head-to-tail, on either side of a central plane (P) and defining two air gaps (E1, E2). Each magnetizing structure (SMM11, SM12) comprises first (AM1) and second (AM2) magnetizing assemblies, whose induction vectors are oriented in opposite directions, and mounted on a support (SUP1). Each magnetizing assembly (AM1, AM2) has a permanent magnet structure (API, APC) which comprises a passive side (FP1, FP2) and an active side (FA1, FA2), delimiting the air gaps (E1, E2). The induction vectors of the first (AM1, AM19) and the second (AM2, AM29) magnetizing assemblies, form inside the generator, a single circulation loop of a magnetic field through the supports (SUP1) and the air gaps (E1, E2, E3, E4).
