A rotation angle detection device comprising: a detection rotor rotating in accordance with rotation of a rotating body and provided with a plurality of magnetic poles; a first magnetic sensor outputting, in accordance with the rotation of the detection rotor, a first output signal (V1=A1·sinθ) that is a sinusoidal signal serving as a reference; and a second magnetic sensor outputting, in accordance with the rotation of the detection rotor, a second output signal (V2=A2·cosθ) that is a sinusoidal signal having a predetermined phase difference with respect to the first output signal; and detecting a rotation angle of the rotating body based on the output signals (V1, V2) of the magnetic sensors (21, 22), the rotation angle detection device further comprising: a storage means storing angular widths of the respective magnetic poles measured in advance; a means setting, for each magnetic pole pair of the plurality of magnetic poles, a division corresponding to an angular width of the magnetic pole pair; a magnetic pole identification means (20, S2-S5) identifying, based on the first output signal, a magnetic pole sensed by the first magnetic sensor; a first computation means (20, S7) computing, based on the first output signal, a first rotation angle (θ RS) that is a rotation angle within the division; a second computation means (20, S9) computing, based on the second output signal, a second rotation angle (θ RC) that is a rotation angle within the division; a third computation means (20, S8) computing a first absolute rotation angle (θ AS) of the detection rotor based on the first rotation angle (θ RS) computed by the first computation means (20, S7), the angular widths of the respective magnetic poles stored in the storage means, and the magnetic pole identified by the magnetic pole identifying means (20, S2-S5); a fourth computation means (20, S10) computing a second absolute rotation angle (θ AC) of the detection rotor based on the second rotation angle (θ RC) computed by the second computation means (20, S9), the angular widths of the respective magnetic poles stored in the storage means, and the magnetic pole identified by the magnetic pole identifying means (20, S2-S5); and a fifth computation means (20, S11, S12, S31, S32, S12A) computing a rotation angle (θ E) of the rotating body based on the first absolute rotation angle (θ AS) computed by the third computation means (20, S8) and the second absolute rotation angle (θ AC) computed by the fourth computation means (20, S10). a storage means storing angular widths of the respective magnetic poles measured in advance; a means setting, for each magnetic pole pair of the plurality of magnetic poles, a division corresponding to an angular width of the magnetic pole pair; a magnetic pole identification means (20, S2-S5) identifying, based on the first output signal, a magnetic pole sensed by the first magnetic sensor; a first computation means (20, S7) computing, based on the first output signal, a first rotation angle (θ RS) that is a rotation angle within the division; a second computation means (20, S9) computing, based on the second output signal, a second rotation angle (θ RC) that is a rotation angle within the division; a third computation means (20, S8) computing a first absolute rotation angle (θ AS) of the detection rotor based on the first rotation angle (θ RS) computed by the first computation means (20, S7), the angular widths of the respective magnetic poles stored in the storage means, and the magnetic pole identified by the magnetic pole identifying means (20, S2-S5); a fourth computation means (20, S10) computing a second absolute rotation angle (θ AC) of the detection rotor based on the second rotation angle (θ RC) computed by the second computation means (20, S9), the angular widths of the respective magnetic poles stored in the storage means, and the magnetic pole identified by the magnetic pole identifying means (20, S2-S5); and a fifth computation means (20, S11, S12, S31, S32, S12A) computing a rotation angle (θ E) of the rotating body based on the first absolute rotation angle (θ AS) computed by the third computation means (20, S8) and the second absolute rotation angle (θ AC) computed by the fourth computation means (20, S10).