Provided is a linear motion guide device comprising a side seal-side space (52) in which a side seal (6) is mounted to a slider (4) and deformation in the slider movement direction is minimized. The side seal (6) comprises a seal lip (48) that comes into slidable contact with an outer surface that includes the rail-side rolling surface (10) of a guide rail. The side seal-side space (52) is arranged more to the slider (4) side than the seal lip (48) and is a space that communicates with a gap (C) formed between the slider (4) and the rail-side rolling surface (10).