Magnetic field generating device and rotating electrical machine

A field magnet holder provided at a field portion of an electric motor is formed of a non-magnetic material. An inner wall and outer wall of the field magnet holder are respectively formed in annular shapes. Plural spacers are arranged between the inner wall and outer wall at a predetermined spacing in the circumferential direction. Sockets into which permanent magnets are inserted are formed between the spacers of the field magnet holder, plurally in the circumferential direction. Therefore, the permanent magnets may be easily assembled by being respectively inserted into the sockets. The plural permanent magnets are arrayed with magnetization directions thereof successively changed in steps of an angle that is a full cycle of electrical angles divided by a division number n, which division number n is any one integer that is at least three. Thus, ease of assembly of the permanent magnets is improved.