A treadmill roller structure comprises a motor, a gear set and a case. The motor is an out-runner motor. The power output section of the motor rotates about stationary spindle. The rotary power output section is engaged to the gear set, while the gear set is in turn engaged to the case, thus allowing the case to rotate relatively to the spindle of the motor as well. The roller structure does not require a driving belt to transfer power from the motor to the roller, thus reduces the power loss due to frictional force during power transfer through belt driving, which enhances the performance of the motor and offers a space-saving feature. In addition, the instant disclosure also provides a treadmill.