PURPOSE: To reduce the manufacturing cost of a thick plate and middle plate and to improve productivity by executing flying cut under specified conditions after cooling a hot rolled steel plate to specified temp. or less on a runout table.

CONSTITUTION: At the time of manufacturing the thick plate and middle plate with a hot rolling mill which is directly connected to a continuous hot rolling mill or a continuous casting machine for thin slabs, by cutting the hot rolled steel plate in running at 400-1500t/h immediately or after cooling it to ≤300°C on the runout table, a base material for thick and middle plates is manufactured and, after that, cut into an ordered length. In this way, the cost of equipment investment is reduced by process saving, also variable cost is reduced by improving productivity and manufacturing cost is decreased.