Abstract: A light-weight linear ball bearing includes an outer casing made of a flat, thin steel plate and having a substantially U-shaped cross-sectional form, an inner casing fitted into the outer casing and having a substantially U-shaped cross-sectional form, and a ball casing made of a flat material. The inner casing is made of a flat, thin steel plate and has flange portions and a central flat portion formed by bending the lateral edge portions of the steel plate with the exception of the two longitudinal end portions thereof. The ball casing has: flat mounting portions formed at the two longitudinal ends thereof, side wall portions engaged with the inner surfaces of the lateral flange portions of the inner casing; and a central wall portion which forms non-loaded ball circulating grooves in cooperation with the side wall portions. The ball casing has ball rolling direction changing grooves formed at the longitudinal ends of each of the side wall portions.