To provide a rolling bearing device of grease lubrication type capable of eliminating inconvenience such that the agitating resistance of rolling elements enlarges in case the grease is replenished anew.

According to the rolling bearing device and a lubricating method for it, not the grease G itself but its base oil 30 is solely replenished to the rolling bearing device 1, so that an increase in the amount of a thickening agent will never occur, and the rise of the agitating resistance of the balls 8 can be suppressed, and at the same time, in particular the conventional inconvenience such as heat emission etc. associated with a shorter lifetime of the grease G in the bearing used in a high speed operation can easily be eliminated.