A linear guide apparatus is provided such that even if the length of an underseal is changed, the adhesion of the underlip and the side lip can be maintained and the lubricant leakage from the slider is preventable. In the linear guide apparatus, the underseal (10) includes a gap seal protrusion part (20) formed to protrude toward a side seal (17) side to seal the gap between the underseal and the side seal. The gap seal protrusion part (20) is integrally formed adjacently to an underlip (10b) of the underseal (10), and is in contact with a terminal end face (17e) of the side lip (17b) of the side seal (17) without a gap.