Abstract: The present invention provides a linear motion clamping unit capable of reliably holding the casing unit at an arbitrary position on the track rail with a small force. In this linear motion clamping unit, when the actuators are deenergized, the rollers arranged in the openings of the retainers are pushed by the spring force through the retainers to engage with the lock portions formed between the inclined surfaces of the wedge members and the side wall surfaces of the track rail. The resulting wedge action locks the casing unit on the track rail in one axial direction. When the actuators are energized, the rollers are released from the lock portions by the action of the retainers, thus unlocking the casing unit.