To provide a screw down device for a rolling mill, a device having desirable features in handling and cost for example by facilitating maintenance of a position detector for detecting rolling reduction and by minimizing the required number of the detectors, and also to provide a rolling mill.

The screw down device 7A for a rolling mill is for screwing down a rolling roll by a hydraulic cylinder 10 while the position is detected. In the hydraulic cylinder 10, there are installed the main rod 12 which extends from the cylinder body 11 toward the rolling roll and in addition a sub rod 13 which penetrates through the end of the cylinder body 11 while extending to the opposite side from the main rod 12 and which is displaced integrally with the main rod 12. A position detector 20 for detecting the position of the sub rod 13 is arranged in an external part of the cylinder body 11.