A workpiece transfer system or method is provided for transferring workpieces one set of pallets to another set of pallets using a workpiece transfer device that is movably attached to a robot. The workpiece transfer device uses mechanical devices to align the workpiece relative to the robot so that different types of workpieces can be placed into a pallet without the need of troublesome, expensive and complex image processing in which the workpiece holding positions are processed as images by using an imaging device such as a visual sensor. Preferably, the workpiece transfer device cooperates with a positional adjustment part such that the workpiece that is held by the transfer device contacts the the positional adjustment part to position the workpiece in a depthwise direction of the workpiece, a widthwise direction of the workpiece and a longitudinal direction of the workpiece.