a guide rail which has a first rolling element rolling groove extending in an axial direction; and

a slider which has a second rolling element rolling groove opposed to the first rolling element rolling groove of the guide rail and is laid across the guide rail so as to relatively move along the axial direction through rolling movements of a plurality of rolling elements disposed between the first rolling element rolling groove and the second rolling element rolling groove,

wherein the slider has:

a slider main body which has a rolling element passage extending through the slider main body in the axial direction and the slider main body having a flat bottom surface;

an end cap which has a direction changing passage in a curved shape for communicating the rolling element passage, a passage formed by the first and second rolling element rolling grooves and a recessed portion, and is fixed to an axial end portion of the slider main body; and

an under seal which is arranged on an under surface of the slider main body along the axial direction, comes in slide contact with the guide rail, and seals the under surface of the slider main body, and the under seal has a core bar which has a common plane which extends parallel to the flat bottom surface of the slider main body, and

the under seal has two rows of elastic lip portions, in a portion of the under seal coming in contact with the slider main body, which have a length approximately equal to an axial length of the slider main body and elastically contact the slider main body;

wherein the elastic lip portions protrude toward the slider main body from the common plane of the under seal, and

wherein the two rows of the elastic lip portions, which oppose to the slider, are provided on the same surface of the under seal.