A rotation-angle detection device includes: an amplitude adjustment unit that performs correction to match amplitude values of multiple detection signals output from multiple rotation detection units to output corrected signals, the rotation detection units changing outputs in accordance with a rotation angle of a rotor and being provided such that the rotation detection units output the detection signals having different phases; a vector generation unit that performs addition and subtraction on two signals out of the corrected signals to generate two vector component signals that are perpendicular to each other; an amplitude correction unit that performs correction to match amplitudes of the two vector component signals to output corrected vector component signals; and a rotation-angle searching unit that searches for the rotation angle of the rotor on basis of a vector that is represented by the two corrected vector component signals to output a detection angle.