Abstract: An articulated vertebral body spacer is constituted by a pair of upper and lower joint pieces to be inserted between vertebras. The lower joint piece includes a convex portion formed on a central portion of its upper surface and having a convex sliding contact surface, and a stopper surface surrounding the convex portion. The upper joint piece includes a concave portion formed on a central portion of its lower surface and having a concave sliding contact surface which is sliding contact with the convex sliding contact surface, and an abutment surface which surrounds the concave portion and abuts against the stopper surface. A cavity for allowing the upper joint piece to pivot in accordance with forward/backward and bending motions of vertebral bodies to respective levels is formed between the abutment surface and the stopper surface.