A rotational angle detection device includes a magnet with n pole pairs (where n≥3) provided to be integrally rotatable with a rotating body; magnetic detection parts including first and second magnetic detection parts; a corrected signal generation part generating first and second corrected signals; and a rotational angle detection part detecting the rotational angle of the rotating body based on the first and second corrected signals. The waveform of the first and second detection signals have a phase difference of 90° from each other. The corrected signal generation part adds the first sensor signals and adds the second sensor signals. The region at the perimeter of the magnet includes first through nth regions, and at least two of the first and second magnetic sensor parts are positioned in different regions from each other among the first through nth regions.