A bicycle torque detector includes a crank shaft formed with a first ring section and a second ring section; the first ring section serving for receiving a deformation sleeve accommodating ring and a deformable sleeve; the second ring section serving for receiving a circuit board ring; a circular casing serving to enclose all the crank shaft, the elastic ring, the sleeve, and the circuit board ring; wherein the first ring section of the crank shaft is formed with at least one resisting portion; the deformable sleeve has at least one resisting portion; the resisting portion of the crank shaft resists against one end of the deformation sleeve accommodating ring; another end of the deformation sleeve accommodating ring resists against the resisting portions of the deformable sleeve. A rear end of the deformable sleeve is engaged to a chain sleeve. The deformation sleeve accommodating ring is adhesive with sensing sheet.