Magnetic gear device and holding member

A magnetic gear device including: an internal rotor and an external rotor in which a plurality of magnetic pole pairs are each placed in a circumferential direction substantially at equal intervals; and a holding member that is placed between the internal rotor and the external rotor and holds a plurality of magnetic materials in the circumferential direction substantially at equal intervals, wherein the number of magnetic materials is a difference between or a total of the numbers of magnetic pole pairs, the holding member includes a plurality of circular rings that hold the magnetic materials, and connecting rods that are placed in the circumferential direction substantially at equal intervals and connect the plurality of circular rings, the plurality of circular rings face each other via the magnetic materials, and each number of magnetic pole pairs is set to have the number of connecting rods as a divisor.