A gear pump (1) includes a pair of gears (4, 5) that meshes with each other, two shafts (2, 3) that are rotationally supported, inserted into the pair of respective gears, and rotate together with the pair of gears, a pair of side plates (7, 7') that is arranged adjacent to both side surfaces of the pair of gears, and each have two through-holes forming bearings of the two shafts, a seal block (8) that abuts against the pair of side plates, and covers a part of the pair of gears in a circumferential direction, a pump assembly (10) having the pair of gears, the two shafts, the pair of side plates, and the seal block, and a case (12) having a recess (12a) in which the pump assembly is accommodated, and having a facing surface (12b) that faces the seal block on an inner wall forming the recess, in which the pump assembly (10) has a line passing through an arc center of a cylindrical surface which is inscribed in the facing surface (12b) of the case, and is parallel to two shafts (2, 3) as a rotating axis, and is hold to be rotatable about the rotating axis, and when the pump assembly rotates about the rotating axis, one of the pair of side plates comes in contact with the inner wall of the case (12).