A linear motion guide unit with a lubricating system made compact or slim in construction with inexpensive production cost and permitted to lubricatesliding contacts with accompanying reduced maintenance. The slider has a tubular member for a return passage to allow rolling elements rolling through there, a lubricant reservoir to accumulate lubricant, and a leading member to transfer the lubricant from the reservoir to the tubular member. The lubricant is supplied from the reservoir into the return passage via the leading member. The lubricant reservoir including an occluding member packed in a cartridge to keep the lubricant inside the cartridge.