To provide a back-up roll device with which the generation of streak marks on a steel sheet or the like of a product is mitigated even when it is used for a tension leveler or the like.

In the back-up roll device 11, a cylindrical roll 13 is installed freely rotatably through ball and roller bearings 14, 15 on the outer periphery of a shaft 12. The intermediate part in the axial direction of the outside diameter surface 13a of the roll 13 is formed into an approximately rectilinear flat part 13aa in a cross-sectional shape and the shaft end parts of the outside diameter surface 13a are taken as a tapered surface drooping part 13ab. The joining part between the flat part 13aa and the surface drooping part 13ab is a projecting curve in the cross-sectional shape and taken as a projecting curve part 13ac which is smoothly connected to the flat part 13aa and the surface drooping part 13ab.