A rotation detecting device comprising: a plurality of magnetic encoders (2A, 2B) arranged in a coaxial ring arrangement and having respective number of magnetic poles different from each other; and a plurality of magnetic sensors (3A, 3B, 3Am, 3Ai) for detecting respective magnetic fields of those magnetic encoders (2A, 2B), each of the magnetic sensors (3A, 3B, 3Am, 3Ai) having a function of detecting information on the position of the magnetic encoders (2A, 2B) within each of the magnetic poles, wherein each of the magnetic sensors (3A, 3B, 3Am, 3Ai) includes a plurality of sensor elements (3A1, 3A2, 3B1, 3B2), and a phase detector (13A, 13B) for determining the phase of the sensor element (3A1, 3A2, 3B1, 3B2) in reference to a magnetic field signal detected thereby and outputting an ABZ phase signal including A-phase and B-phase pulse signals A and B, which are displaced 90° in phase from each other, and a Z-phase pulse signal Z indicative of start position wherein at least one of the plurality of magnetic encoders (2A, 2B) having different numbers of magnetic poles includes a plurality of magnetic tracks (2Am, 2Ai), a portion of the magnetic tracks (2Am, 2Ai) being formed with a phase offset pattern generating an index signal; and the rotation detecting device further comprising: a phase difference detector for determining a phase difference of the magnetic field signals in reference to an output from the phase detector (13A, 13B); and an angle calculator (7, 12) for calculating the absolute angle of the magnetic encoders (2A, 2B) based on the phase difference so detected, characterized in that the phase detector (13A, 13B) comprises an absolute angle output mode execution section capable of providing an output by selecting one of an absolute angle output mode, in which the phase of the magnetic field signal is outputted as the absolute angle, and a normal mode in which only the A-phase and B-phase pulse signals A and B are outputted, and wherein the absolute angle output mode is a mode executed from powering on or from receiving a predetermined signal until attaining a latest phase of the magnetic field, and shifts to the normal mode once the latest phase of the magnetic field is attained. a plurality of magnetic encoders (2A, 2B) arranged in a coaxial ring arrangement and having respective number of magnetic poles different from each other; and a plurality of magnetic sensors (3A, 3B, 3Am, 3Ai) for detecting respective magnetic fields of those magnetic encoders (2A, 2B), each of the magnetic sensors (3A, 3B, 3Am, 3Ai) having a function of detecting information on the position of the magnetic encoders (2A, 2B) within each of the magnetic poles, wherein each of the magnetic sensors (3A, 3B, 3Am, 3Ai) includes a plurality of sensor elements (3A1, 3A2, 3B1, 3B2), and a phase detector (13A, 13B) for determining the phase of the sensor element (3A1, 3A2, 3B1, 3B2) in reference to a magnetic field signal detected thereby and outputting an ABZ phase signal including A-phase and B-phase pulse signals A and B, which are displaced 90° in phase from each other, and a Z-phase pulse signal Z indicative of start position wherein at least one of the plurality of magnetic encoders (2A, 2B) having different numbers of magnetic poles includes a plurality of magnetic tracks (2Am, 2Ai), a portion of the magnetic tracks (2Am, 2Ai) being formed with a phase offset pattern generating an index signal; and a phase difference detector for determining a phase difference of the magnetic field signals in reference to an output from the phase detector (13A, 13B); and an angle calculator (7, 12) for calculating the absolute angle of the magnetic encoders (2A, 2B) based on the phase difference so detected, the phase detector (13A, 13B) comprises an absolute angle output mode execution section capable of providing an output by selecting one of an absolute angle output mode, in which the phase of the magnetic field signal is outputted as the absolute angle, and a normal mode in which only the A-phase and B-phase pulse signals A and B are outputted, and wherein the absolute angle output mode is a mode executed from powering on or from receiving a predetermined signal until attaining a latest phase of the magnetic field, and shifts to the normal mode once the latest phase of the magnetic field is attained.