PURPOSE: To satisfactorily maintain a bearing at all times by providing a drain path for lubricating oil from the bearing and a means for measuring the pressure and flow of transporting gas in the drain path so that the supply condition of the lubricating oil to individual bearings disposed in various facilities can be monitored.

CONSTITUTION: A lubricating oil supply system 10 is provided to supply lubricating oil to bearings 16, 18, 20 and 22 shaft-supporting a plurality of rollers 12, 14 such as casting piece support rollers disposed in a secondary cooling zone of a continuous casting machine and rolling rollers disposed in a hot or cold rolling mill for steel material. Then, drain paths 34, 36 and 40 for draining the lubricating oil (waste lubricating oil) supplied to the respective bearings and oberflowing therefrom are provided respectively with pressure gauges 42, 44, 46 and 48 for measuring the pressure of transportation air passing through the bearings. The supply conditions of the lubricating oil to the respective bearings are monitored according to the measuring results to judge the choking in the transportation pipe, disengagement thereof or the like.