A small, high-stiffness torque sensor. An annular deformable body is disposed between left and right side supports. Convex sections protruding from the left side support in a rightward direction are joined to the left side surface of the annular deformable body, and convex sections protruding from the right side support in a leftward direction are joined to the right side surface of the annular deformable body. When force is applied to the right side support and torque around the Z axis acts on the left side support, the annular deformable body is elliptically deformed and the long-axis position of the inner peripheral surface of the annular deformable body moves away from the Z axis while the short-axis position moves closer to the Z axis. The acting torque is detected as a variation in the capacitance value of capacitive elements formed by displacement electrodes and fixed electrodes.