Linear bearing and linear bearing with housing

A linear-motion bearing, comprising:

• an outer cylinder member made of a synthetic resin, the 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, which has an arc cross section, and is fitted to each of the planar spaces, the synthetic resin plate including a metal piece at a position at which the synthetic resin plate is held in contact with a steel ball row in the inner-peripheral-side steel ball circulation path, the metal piece having an elongated shape in a direction along the steel ball row in the inner-peripheral-side steel ball circulation path,
• wherein 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.