Magnetic gears are able to transmit torque without mechanical contact. Therefore, these have attractive features, such as low acoustic noise and maintenance-free operation in comparison with conventional mechanical gears. Planetary-type magnetic gears, especially, have higher transmission torque than the other types, and are expected to be put into practical use. This paper presents a method for calculating dynamic characteristics of the magnetic gear based on reluctance network analysis (RNA). The RNA has several features, including a simple analytical model, high calculation accuracy, and ease of coupled analysis with rotational motion of rotors.