Abstract: A magnetic braking apparatus is integrally attached with a load detector such as an arm-like load cell through an attachment member, an outer fin, or a rotary joint between a yoke body and a stationary portion of an outside construction or facility thereby to form a magnetic braking apparatus having a function of load detection. A tension control system incorporates the magnetic braking apparatus with the load detector attached thereto to apply a braking force to a let-off reel. A controller in the tension control system calculates a roll diameter of the let-off reel based on a number of rotations detected by a rotation detector and a number of pulses generated in one rotation of the let-off reel, and generates a control signal representative of a desired braking torque which corresponds to the calculated roll diameter.