A lubrication apparatus for the ball screw unit in which the grease state lubricant is used. There is formed a helical guide track in the lubrication apparatus. When the ball screw unit operates, a guide member rotates with the bolt, the grease stored in the guide track will flow ahead to the front terminal of the guide track and ooze out of the grease outlet to lubricate the bolt with the aid of a pressure produced due to the inertia of the flowing fluid, and the quantity of the oozed grease is determined by the size of the grease outlet. The lubrication of the ball screw unit can be performed automatically without relying on the external force.