A gear pump comprising: - a first gear, which is fixed on a freely rotatable first support shaft and which rotates together with said first support shaft; - a second gear, which is supported rotatable on a second support shaft disposed parallel to said first support shaft and which meshes with said first gear; and - a casing, which provides an installation space for accommodation of said first gear and said second gear and which supports said first support shaft rotatable and supports said second support shaft; wherein: - said casing is provided with an intake port, which is in fluid communication with said installation space, and with a discharge port, which is in fluid communication with said installation space; - said first gear and said second gear meshing with each other are rotated by the rotation of said first support shaft, so that a fluid is sucked through said intake port into said gear pump and discharged therefrom through said discharge port; characterized in that: said gear pump further comprises a gear holder, which supports said second gear rotatable and holds both sides of said second gear in said installation space, said gear holder is supported and mounted axially movable on said second support shaft; and - while said gear holder is being subjected to an axial biasing force from a biasing member provided on one side in the axial direction of the support shafts (30, 60), said gear holder is subjected also to a pressing force that acts against said biasing force, on the other side in the axial direction of the support shafts (30, 60), which results in said gear holder holding said second gear being moved in the axial direction of the support shafts (30, 60). - a first gear, which is fixed on a freely rotatable first support shaft and which rotates together with said first support shaft; - a second gear, which is supported rotatable on a second support shaft disposed parallel to said first support shaft and which meshes with said first gear; and - a casing, which provides an installation space for accommodation of said first gear and said second gear and which supports said first support shaft rotatable and supports said second support shaft; - said casing is provided with an intake port, which is in fluid communication with said installation space, and with a discharge port, which is in fluid communication with said installation space; - said first gear and said second gear meshing with each other are rotated by the rotation of said first support shaft, so that a fluid is sucked through said intake port into said gear pump and discharged therefrom through said discharge port; characterized in that: said gear pump further comprises a gear holder, which supports said second gear rotatable and holds both sides of said second gear in said installation space, said gear holder is supported and mounted axially movable on said second support shaft; and - while said gear holder is being subjected to an axial biasing force from a biasing member provided on one side in the axial direction of the support shafts (30, 60), said gear holder is subjected also to a pressing force that acts against said biasing force, on the other side in the axial direction of the support shafts (30, 60), which results in said gear holder holding said second gear being moved in the axial direction of the support shafts (30, 60).