A rotation preventing/thrust bearing device for an orbiting member type fluid displacement apparatus prevents rotation of an orbiting member during orbital motion and carries axial loads from the orbiting member. The rotation preventing/thrust bearing device of the present invention includes a fixed ring which is attached to a housing and an orbit ring which faces the fixed ring and is attached to an end surface of the orbiting piston. These rings have a plurality of corresponding pockets which face each other. Each pocket on the fixed ring faces a pocket on the orbiting ring corresponding in size, pitch and radial distance from the center of the respective rings. A predetermined number of these pockets function as rotation prevention pockets; these rotation prevention pockets have a diameter or size slightly smaller than the remaining pockets. These rotation preventing pockets cooperate with spherical balls, one of which is placed within each facing pair of corresponding pockets, to prevent rotation of the orbiting piston. Thus, while all the spherical balls carry axial loads, only a predetermined number interact with the pockets to prevent rotation of the orbiting member. This predetermined number is greater than or equal to three but smaller than the total number of balls and pockets.