A rotation detection device includes a plurality of magnetic encoders of a ring shape arranged coaxially and having different numbers of magnetic poles, a plurality of magnetic sensors each operable to detect the magnetic field of the corresponding magnetic encoder and having a function of detecting positional information within a single magnetic pole of the corresponding magnetic encoder, a phase difference detector to determine the phase difference of magnetic field signals detected respectively by the magnetic sensors, and an angle calculator to calculate an absolute rotation angle of the magnetic encoders based on the detected phase difference.