A rotation sensor including: a main rotor that integrally rotates with a rotor to be measured; a sub-rotor that rotates in accordance with rotation of the main rotor with a different number of revolutions from that of the main rotor; a first detector detecting rotation of the main rotor; and a second detector detecting rotation of the sub-rotor. The rotation sensor detects an absolute rotation angle of the rotor to be measured from detection signals from the first detector and the second detector. Respective detection signals obtained from the first detector and the second detector are cyclically output in accordance with rotation of each rotor, and the following relationship is satisfied: (Tm−Tc×i)×n=Tm (i and n are positive integers), wherein Tc is a cycle of the detection signal from the first detector, and Tm is a cycle of the detection signal from the second detector.