A treading torque detection device includes a pre-set trading torque and a motor. The torque from the pre-set trading torque and the torque from the motor are respectively connected to a hollow tube mounted to an axle via a first one-way transmission device and a second one-way transmission device. The two respective powers are transmitted to a chainwheel by the hollow tube. A torque detection unit us connected to the hollow tube and located between the first and second one-way transmission devices. The power from the motor and the treading torques from the two ends of the axle do not affect to each other. When the torque detection unit detects a torque that is higher than the pre-set trading torque, the motor is activated to provide power, and the detected torque is reduced to the pre-set torque.