A motion guide device (1) includes: a track body that extends in a longitudinal direction; a movable body (20) that is mounted on the track body and is movable along the track body; an encoder scale that is disposed at the track body in the longitudinal direction; a sensor (50) that is disposed opposite to the encoder scale; and a folder (60) that is disposed at an end face of the movable body (20) in the longitudinal direction, houses the sensor (50) in a width direction of the track body, and holds the sensor such that the sensor faces the encoder scale.

A linear motion guide unit includes a rail including a rail upper surface and a rail side surface each extending in a longitudinal direction and having a first raceway surface provided on the rail side surface, a sliding member relatively movably attached to the rail and including a sliding member lower surface facing the rail upper surface and a second raceway surface facing the first raceway surface, a plurality of rolling elements rolling on a load-carrying race constituted by the first and second raceway surfaces, a cover member covering the rail and the sliding member and including a first fastener extending in the longitudinal direction, a moving member arranged outside the cover member and moving together with the sliding member, and a connecting member connecting the sliding member to the moving member. The first fastener includes a first right side element extending along the longitudinal direction, a first left side element extending in the longitudinal direction along the first right side element and engageable with the first right side element, a first front slider attached to the first right side element and the first left side element and fixed to the sliding member and the moving member, and a first rear slider attached to the first right side element and the first left side element, spaced apart from the first front slider in the longitudinal direction, and fixed to the sliding member and the moving member. During movement of the sliding member and the moving member, the first front slider and the first rear slider each disengage the first right side element and the first left side element from each other while the slider moves in a direction opposite to a side where the other slider is located, and engage the first right side element and the first left side element with each other while the slider moves in a direction toward the side where the other slider is located. The connecting member includes a first support member arranged between the first front slider and the first rear slider in the longitudinal direction and supporting the moving member. As viewed from the rail upper surface side in a direction perpendicular to the longitudinal direction, a first opening region resulting from disengagement between the first right side element and the first left side element is placed in a position avoiding the rail.

A linear motion unit includes: a linear motion mechanism including a track member and a moving member; and a housing including a fastener. The fastener includes a first element, a second element meshable with the first element, a first slider, and a second slider located away from the first slider in longitudinal directions. The first slider and the second slider cause the first element and the second element to be separated from each other when the first slider and the second slider move away from each other, and cause the first element and the second element to mesh with each other when the first slider and the second slider move toward each other. The first slider and the second slider are fixable to the moving member.