A pallet changing system for a machine tool includ­ing a pallet changing device which is horizontally rotatable for exchanging a pallet on the work table of the tool with another pallet in a standby station. A plurality of pallet storing shelves are arranged in a plurality of con­centric circular arrays and each shelf has a plurality of pallet supporting racks located one above another. The standby station forms a part of those circular arrays defin­ing a central space surrounded by the racks. A rotary table is rotatably disposed in the center of that space. A pair of guide posts are upstanding from the rotary table. A structure is vertically movably supported on the posts. A pallet handling fork is provided on the structure hori­zontally movably to and away from the standby station. A pair of guide rails guide the horizontal movement of the fork. The fork has one end defining a pallet supporting portion. The system further includes a device for rotat­ing the rotary table in an indexed way, a device for mov­ing the vertically movable structure vertically and a device for moving the fork horizontally.