To enable high-draft rolling for suppressing load at the time of biting.

Rolling speed V1 is set beforehand to be slower than predetermined rolling speed V2 and also the opening degree between rolls is made larger than the preset. In this state, by gradually reducing the opening degree between the rolls while forcing the tip of a material 3 to be rolled between the rolls 1, the opening degree is constituted so as to become the set opening degree when the tip of the material 3 to be rolled reaches a position just under of the roll 1 and, at the point of time when the opening degree becomes the set opening degree, the rolling speed V1 is increased and returned to the preset rolling speed V2.