Cooling device for hot rolled steel sheet and cooling method for the same

A cooling device cooling an undersurface of a hot rolled steel sheet that is being transported on transport rolls after finish rolling of a hot rolling step, the cooling device comprising:

• width divided cooling zones that are a plurality of cooling zones into which a whole cooling zone is divided in a sheet width direction, the whole cooling zone being a cooling zone partitioned by all of a width of an undersurface of a sheet transport zone in the sheet width direction and a predetermined length of the undersurface of the sheet transport zone in a rolling direction;
• divided cooling sections that are a plurality of cooling zones into which each of the width divided cooling zones is divided in the rolling direction;
• at least one cooling water nozzle spraying cooling water over each of undersurfaces of the divided cooling sections;
• a switching mechanism switching the cooling water sprayed from the cooling water nozzle between impinging and not impinging on the divided cooling sections;
• a width direction thermometer measuring a temperature distribution in the sheet width direction;
• and
• a controller controlling operation of the switching mechanism based on a result of measurement with the width direction thermometer.