A foreign-substance discharge mechanism includes: a lubricating-liquid groove provided on a sliding surface of a wedge member and configured to receive a lubricating liquid; and a foreign-substance collector provided to the lubricating-liquid groove and configured to collect foreign substances existing in the lubricating-liquid groove. A first end and a second end of the lubricating-liquid groove are spaced apart from each other in a relative movement direction of the wedge member and the table bed. Disadvantages caused by the presence of the foreign substances between the sliding surfaces can be easily avoided by reliably collecting the foreign substances existing between the sliding surfaces using the lubricating-liquid groove and the foreign-substance collector.