Abstract: A linear-motion bearing is disclosed including: an outer cylinder member having a plurality of endless steel ball circulation paths each including an outer-peripheral-side steel ball circulation path and an inner-peripheral-side steel ball circulation path, and having planar spaces in regions that are opposed to the endless steel ball circulation paths, respectively; a plurality of steel balls accommodated and arrayed in the endless steel ball circulation paths: and a synthetic resin plate including a metal piece at which the synthetic resin plate is held in contact with a steel ball row, the metal piece having an elongated shape in a direction along the steel ball row in the inner-peripheral-side steel ball circulation path, in which the elongated metal piece is curved so as to protrude toward an inner peripheral side of the outer cylinder member in the direction along the steel ball row in the inner-peripheral-side steel ball circulation path.