PURPOSE: To provide a magnetic field generating device in which the mutual influence of coils is structurally prevented, also current consumption in normal state is small, and the rising characteristics of the magnetic field is improved.

CONSTITUTION: In the magnetic field generating device in which the coil 1, magnetic yoke 2, 3 equipped in relation to the coil, and a driving circuit 30 for energizing the above coil 1 are provided, the coil 1 is composed of plural coils of the same common composition as for the magnetic yokes 2, 3. The driving circuit 30 is constituted of switching means (a)-(e), by which the energizing to the coil is switched either in parallel or in series, and a means 31 so as to drive under a constant current in series.