PURPOSE: To prevent the slant travelling of a rolling material by providing the parallel position commander giving a slant travelling correcting quantity according to the slant travelling of a rolling material and by arranging the 2nd roll position setter setting up a vertical roll at the prescribed position.

CONSTITUTION: The 2nd roll position setters 3, 4 moving in parallel to the progressing direction of a rolling material 16 are arranged in addition to the 1st roll position setters 12, 13 performing the positioning vertical to the progressing direction of the rolling material 16. The 2nd position setters 3, 4 give to controlling devices 7, 8 the reference to change the right and left roll positions by a parallel position commander 9 according to the differential pressure of an end face detectors 17, 18 when the slant travelling is caused by the rolling material 16. The controlling devices 7, 8 drive the 2nd position setters 3, 4 by driving devices 5, 6 based on said reference quantity. Rolls 1, 2 are moved according to the slant travelling with said method and the slant travelling of the rolling material 16 is prevented.