There is provided a lubricating method for a rolling bearing assembly capable of achieving a reliable lubrication and exhibiting a stable temperature rise. The method is for supplying a lubricant oil to the rolling bearing assembly during the operation thereof, in which in order to keep the temperature of a rolling bearing assembly (103) within a predetermined tolerance, the amount of the lubricant oil to be supplied during the operation is automatically or manually adjusted by means of a supply adjusting unit (102). Supply of the lubricant oil is performed in the form of an air/oil mixture by the use of a lubricant supply unit (101). The amount of the lubricant oil supplied varies depending on the rotational speed of the rolling bearing assembly (103). Change of the amount of the lubricant oil supplied depending on the rotational speed of the rolling bearing assembly (103) is carried out based on a result of sampling of data showing increase in temperature of the rolling bearing assembly (103) depending on the rotational speed thereof under a plurality of different lubricating conditions in which a different amount of the lubricant oil to be supplied is employed.