A gear pump includes a pair of gears that meshes with each other, two rotational shafts inserted into the respective gears that rotate together with gears, a pair of side plates arranged adjacent to both side surfaces of the gears, each having two through-holes forming bearings of the two shafts, a seal block that abuts against the pair of side plates and covers a part of the pair of gears, a pump assembly having the gears, the two shafts, the pair of side plates, and the seal block, and a case having a recess to accommodate the pump assembly. A line passing through an arc center of a cylindrical surface inscribed in the facing surface of the case, and parallel to the two shafts, forms a rotating axis. When the pump assembly rotates about the rotating axis, one of the of side plates contacts the inner wall of the case.