A pallet changing system which utilizes the moving function itself of a machine head at a machining center for conveying a pallet and a configuration of a machining center equipping the system, combines a machine head 2 for machining a workpiece with a pallet changing unit 1 having a pallet changing arm 11 which can be rotated by a motor 13 and then allowed to move, by which a pallet 3 is conveyed, and the new pallet 3 for changing is changed with the existing pallet 3 gripped by a pallet clamping device 4 by turning the pallet changing arm 11, and a machining center which equips the above system and also machines a workpiece by using the machine head 2.