Abstract: A rotation angle sensor including a variable capacitor and a C-V converting circuit, wherein the variable capacitor has a detected object fastened and fixed to its shaft, a planar shape of a movable electrode is set so that an area of overlapping parts of electrodes changes linearly with respect to a change of the rotation angle of the movable electrode, a voltage signal of the C-V converting circuit corresponds to the change of the electrostatic capacity of the variable capacitor with respect to the fixed capacitor, and consequently the voltage signal of the C-V converting circuit (detection signal) can be made to change linearly with respect to broad changes of the rotation angle of the detected object (0° to 270°).