A hydraulic pump having: a rotary shaft rotatably supported with respect to a casing , and a bearing part provided to one end side and the other end side of the rotary shaft wherein the bearing part on the one side has a support part which rotatably supports the rotary shaft characterized by a first annular member provided around the rotary shaft on at least one side of the one end side and the other end side of the rotary shaft , with an inner diameter of the first annular member being larger than a diameter of the rotary shaft so that the first annular member is freely rotatable with respect to an outer peripheral surface of the rotary shaft, wherein the bearing part on the one side further has a preload applying member which is interposed between the support part and the first annular member in the axial direction and applies a preload in the axial direction to the support part , and wherein the first annular member is interposed between the bearing part of the one side and a receiving part of the rotary shaft in the axial direction, being in contact with the preload applying member and the receiving part of the rotary shaft , the receiving part on the one end side has a receiving surface on the one side, a stepped portion with the diameter of the rotary shaft changed being adopted as the receiving surface , and a receiving part on the other end side has a receiving surface on the other side, and wherein the receiving part and the first annular member are adjusted with respect to one another such that, during high speed rotation of the rotary shaft , the first annular member rotates with a number of revolutions being suppressed as compared to the number of revolutions of the rotary shaft . a rotary shaft rotatably supported with respect to a casing , and a bearing part provided to one end side and the other end side of the rotary shaft wherein the bearing part on the one side has a support part which rotatably supports the rotary shaft characterized by a first annular member provided around the rotary shaft on at least one side of the one end side and the other end side of the rotary shaft , with an inner diameter of the first annular member being larger than a diameter of the rotary shaft so that the first annular member is freely rotatable with respect to an outer peripheral surface of the rotary shaft, wherein the bearing part on the one side further has a preload applying member which is interposed between the support part and the first annular member in the axial direction and applies a preload in the axial direction to the support part , and wherein the first annular member is interposed between the bearing part of the one side and a receiving part of the rotary shaft in the axial direction, being in contact with the preload applying member and the receiving part of the rotary shaft , the receiving part on the one end side has a receiving surface on the one side, a stepped portion with the diameter of the rotary shaft changed being adopted as the receiving surface , and a receiving part on the other end side has a receiving surface on the other side, and wherein the receiving part and the first annular member are adjusted with respect to one another such that, during high speed rotation of the rotary shaft , the first annular member rotates with a number of revolutions being suppressed as compared to the number of revolutions of the rotary shaft . <EOS>