Abstract: The present invention provides a rolling roller for rolling steel sections and that can have the roller width changed while not having a drive mechanism for changing the roller width provided to the rolling roller itself, thereby having a simple structure that facilitates exchange, and also provides a rolling mill suitable for use with such a rolling roller. The rolling roller has rolling wheels on a roller shaft and a sleeve and that engage the sleeve with respect to the roller shaft. In addition, the sleeve and the roller shaft are tightened and engaged at a place other than the inner side of the roller wheel and oil injection to the place of tightening and engagement is performed via hydraulic fluid supply paths formed inside the roller shaft.