A torque sensor comprising: an envelope tube, a middle cylinder axially mounted through the envelope tube, an inner cylinder axially mounted through the middle cylinder, at least one outer bearing mounted around and between the envelope tube and the middle cylinder, at least one inner bearing mounted around and between the middle cylinder and the inner cylinder, a resilient element (16, 16A) being compressible, disposed between the middle cylinder and the inner cylinder and having two ends respectively connected to the middle cylinder and the inner cylinder, a first disc being annular, and mounted around and attached to the inner cylinder, a second disc being annular, mounted around the inner cylinder, disposed adjacent to the first disc and attached to the middle cylinder, and a detection unit mounted on the envelope tube and detecting shift angle difference between the first disc and the second disc, and the torque sensor characterized in that: the middle cylinder has a first stop (124, 124A) formed on an inner surface of the middle cylinder; and a second stop (125, 125A) formed on the inner surface of the middle cylinder and separated from the first stop (124, 124A) of the middle cylinder; and the inner cylinder has a first stop (134, 134A) formed on an outer surface of the inner cylinder, and disposed between the first and second stops (124, 124A, 125, 125A) of the middle cylinder; and a second stop (135, 135A) formed on the outer surface of the inner cylinder, separated from the first stop (134, 134A) of the inner cylinder, disposed between the first stop (134, 134A) of the inner cylinder and the second stop (125, 125A) of the middle cylinder and selectively abutting the second stop (125, 125A) of the middle cylinder; wherein when the inner cylinder (13, 13A) rotates, the inner cylinder (13, 13A) pushes the resilient element (16, 16A) and the middle cylinder (12, 12A) sequentially so the resilient element (16, 16A) is compressed and the middle cylinder (12, 12A) rotates accordingly; when no force is applied to the torque sensor, the resilient element causes the second stops (135, 125) of the inner cylinder and the middle cylinder abut each other. the middle cylinder has a first stop (124, 124A) formed on an inner surface of the middle cylinder; and a second stop (125, 125A) formed on the inner surface of the middle cylinder and separated from the first stop (124, 124A) of the middle cylinder; and a first stop (124, 124A) formed on an inner surface of the middle cylinder; and a second stop (125, 125A) formed on the inner surface of the middle cylinder and separated from the first stop (124, 124A) of the middle cylinder; and the inner cylinder has a first stop (134, 134A) formed on an outer surface of the inner cylinder, and disposed between the first and second stops (124, 124A, 125, 125A) of the middle cylinder; and a second stop (135, 135A) formed on the outer surface of the inner cylinder, separated from the first stop (134, 134A) of the inner cylinder, disposed between the first stop (134, 134A) of the inner cylinder and the second stop (125, 125A) of the middle cylinder and selectively abutting the second stop (125, 125A) of the middle cylinder; a first stop (134, 134A) formed on an outer surface of the inner cylinder, and disposed between the first and second stops (124, 124A, 125, 125A) of the middle cylinder; and a second stop (135, 135A) formed on the outer surface of the inner cylinder, separated from the first stop (134, 134A) of the inner cylinder, disposed between the first stop (134, 134A) of the inner cylinder and the second stop (125, 125A) of the middle cylinder and selectively abutting the second stop (125, 125A) of the middle cylinder; wherein when the inner cylinder (13, 13A) rotates, the inner cylinder (13, 13A) pushes the resilient element (16, 16A) and the middle cylinder (12, 12A) sequentially so the resilient element (16, 16A) is compressed and the middle cylinder (12, 12A) rotates accordingly; when no force is applied to the torque sensor, the resilient element causes the second stops (135, 125) of the inner cylinder and the middle cylinder abut each other.