A tension controller for a warping machine maintains a constant yarn tension during a warping operation from the beginning to the end of the warping operation. The tension controller has a brake force control mechanism (240) for controlling the size of the tension applied to the running yarns, and a yarn speed control mechanism (290) for controlling the running speed of the yarns. The brake control input, which is supplied to the yarns brakes, and the running speed of the yarns are so controlled that the actual yarn tension conforms to set or desired tension. When the diameters of the yarn packages are relatively large, a brake force is applied to the yarns, which run at a constant speed, thereby maintaining a constant yarn tension. When the diameters of the yarn packages are relatively small, on the other hand, a constant yarn tension is maintained by reducing the running speed of the yarns while supplying a zero or constant brake force to the yarns.