A rotation detecting device which comprises: a plurality of magnetic encoders (2A, 2B) of a ring shape arranged coaxially and having different numbers of magnetic poles; a plurality of magnetic sensors (3A, 3B) 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 for determining the phase difference of magnetic field signals detected respectively by the magnetic sensors; and an angle calculator for calculating an absolute rotation angle of the magnetic encoders based on the detected phase difference, wherein each of the magnetic sensors comprises a line sensor (3AA, 3AB), in which a plurality of sensor elements are lined up in a direction conforming to the direction in which the magnetic poles of the corresponding magnetic encoder are arranged and is operable to detect the position within the single magnetic pole by generating two phase signal outputs forming sine and cosine curves by calculation, wherein the plurality of sensor elements are arranged in offset relation relative to each other within a pitch between the neighboring magnetic poles of the associated line sensor (3AA, 3AB), wherein phase detection circuits (13A, 13B) associated respectively with the line sensors (3AA, 3AB) are provided to detect a phase of the sensor elements to output phase signals, wherein the phase difference detector is operable based on the detected phase signals to detect the phase difference, wherein the rotation detection device further comprises an angle information output circuit for outputting the absolute angle, calculated by the angle calculator, in the form of an ABZ phase signal comprised of two, A phase and B phase pulse signals which are displaced 90° in phase relative to each other and a Z phase pulse signal indicative of a position of origin, the angle information output circuit including a mode execution signal generator generating a mode execution signal indicative of the absolute angle output mode, wherein the absolute angle output mode starts in response to a request signal requesting an absolute angle to be outputted, the request signal being supplied from a receiving side circuit to an angle information output circuit, the receiving side circuit including a position counter indicative of an absolute angle value, the position counter being reset to zero in response to receipt of the Z phase signal, and wherein once pulse outputs of the A phase signal and the B phase signal reach the current absolute angle value, the absolute angle output mode terminates. a plurality of magnetic encoders (2A, 2B) of a ring shape arranged coaxially and having different numbers of magnetic poles; a plurality of magnetic sensors (3A, 3B) 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 for determining the phase difference of magnetic field signals detected respectively by the magnetic sensors; and an angle calculator for calculating an absolute rotation angle of the magnetic encoders based on the detected phase difference, wherein each of the magnetic sensors comprises a line sensor (3AA, 3AB), in which a plurality of sensor elements are lined up in a direction conforming to the direction in which the magnetic poles of the corresponding magnetic encoder are arranged and is operable to detect the position within the single magnetic pole by generating two phase signal outputs forming sine and cosine curves by calculation, wherein the plurality of sensor elements are arranged in offset relation relative to each other within a pitch between the neighboring magnetic poles of the associated line sensor (3AA, 3AB), wherein phase detection circuits (13A, 13B) associated respectively with the line sensors (3AA, 3AB) are provided to detect a phase of the sensor elements to output phase signals, wherein the phase difference detector is operable based on the detected phase signals to detect the phase difference, wherein the rotation detection device further comprises an angle information output circuit for outputting the absolute angle, calculated by the angle calculator, in the form of an ABZ phase signal comprised of two, A phase and B phase pulse signals which are displaced 90° in phase relative to each other and a Z phase pulse signal indicative of a position of origin, the angle information output circuit including a mode execution signal generator generating a mode execution signal indicative of the absolute angle output mode,