A torque sensor includes: an annular deformation body; first and second displacement electrodes which cause displacement by elastic deformation of the annular deformation body; first and second fixed electrodes arranged at positions opposite the first and second displacement electrodes; and a detection circuit that outputs an electric signal indicating a torque based on a variation amount of capacitance values of first and second capacitive elements each of which is configured of the displacement electrode and the fixed electrode. The annular deformation body includes a high elastic portion and a low elastic portion having a spring constant smaller than a spring constant of the high elastic portion. The detection circuit determines whether the torque sensor functions normally based on a ratio between first and second electric signals.