A fretting-corrosion-prevention oscillating vane type pump actuator, comprising: a cylinder; a pair of side covers (1c, 2c) provided on opposite ends of the cylinder; an oscillating shaft supported by central portions of the pair of side covers (1c, 2c), the oscillating shaft protruding outwards from one side cover; a fixed rotor fitted over the oscillating shaft; an oscillating vane (7c-a, 7c-b) integrated on the rotor; a fixed vane (9c-a, 9c-b) fixed to the cylinder and brought into close contact with the cylinder and the pair of side covers (1c, 2c) by fixed seals (40c-1, 40c-2; 41c-1, 41c-2, 41c-3), the fixed vane (9c-a, 9c-b) having a slide surface (19c-a, 19c-b) that makes contact with a circumferential outer surface of the rotor by means of a slide seal (42c-1, 42c-2); and opposite working chambers (11c-a, 11c-b; 12c-a, 12c-b) having opposing hydraulic pressures, characterized in that, the cylinder is shorter at opposite ends thereof than a length of the rotor, the opposite ends being shorter by a same length, and the pair of side covers (1c, 2c) are integrated with respective cylindrical parts (1c-c, 2c-c) which extend inwards by a same length by which the lengths of the opposite ends of the cylinder are shortened, to compensate for the shorter length of the cylinder, wherein a passage passing through the fixed vane (9c-a, 9c-b) is open on junction surfaces between the fixed vane (9c-a, 9c-b) and the opposite side covers (1c, 2c), and the passage further communicating with the opposite working chambers (11c-a, 11c-b; 12c-a, 12c-b) having the opposing hydraulic pressures, a pair of check valves (21, 22) passing through the passage are installed towards the opposite working chambers (11c-a, 11c-b; 12c-a, 12c-b) having the opposing hydraulic pressures, each of the pair of check valves (21, 22) being oriented in a direction which prevents communication with the working chamber (11c-a, 11c-b; 12c-a, 12c-b) at a high pressure side and allows communication with the working chamber (11c-a, 11c-b; 12c-a, 12c-b) at a low pressure side. a cylinder; a pair of side covers (1c, 2c) provided on opposite ends of the cylinder; an oscillating shaft supported by central portions of the pair of side covers (1c, 2c), the oscillating shaft protruding outwards from one side cover; a fixed rotor fitted over the oscillating shaft; an oscillating vane (7c-a, 7c-b) integrated on the rotor; a fixed vane (9c-a, 9c-b) fixed to the cylinder and brought into close contact with the cylinder and the pair of side covers (1c, 2c) by fixed seals (40c-1, 40c-2; 41c-1, 41c-2, 41c-3), the fixed vane (9c-a, 9c-b) having a slide surface (19c-a, 19c-b) that makes contact with a circumferential outer surface of the rotor by means of a slide seal (42c-1, 42c-2); and opposite working chambers (11c-a, 11c-b; 12c-a, 12c-b) having opposing hydraulic pressures, the cylinder is shorter at opposite ends thereof than a length of the rotor, the opposite ends being shorter by a same length, and the pair of side covers (1c, 2c) are integrated with respective cylindrical parts (1c-c, 2c-c) which extend inwards by a same length by which the lengths of the opposite ends of the cylinder are shortened, to compensate for the shorter length of the cylinder, wherein a passage passing through the fixed vane (9c-a, 9c-b) is open on junction surfaces between the fixed vane (9c-a, 9c-b) and the opposite side covers (1c, 2c), and the passage further communicating with the opposite working chambers (11c-a, 11c-b; 12c-a, 12c-b) having the opposing hydraulic pressures, a pair of check valves (21, 22) passing through the passage are installed towards the opposite working chambers (11c-a, 11c-b; 12c-a, 12c-b) having the opposing hydraulic pressures, each of the pair of check valves (21, 22) being oriented in a direction which prevents communication with the working chamber (11c-a, 11c-b; 12c-a, 12c-b) at a high pressure side and allows communication with the working chamber (11c-a, 11c-b; 12c-a, 12c-b) at a low pressure side.