In a suction device, a suction head is alternately connected to a negative pressure source and a positive pressure source by means of a switching valve, a light-weight workpiece is sucked by and released from the suction head. When the suction head and the positive pressure source are connected to each other by means of the switching valve to release the workpiece, a releasing pressure is instantaneously supplied to the suction head. The magnitude of the releasing pressure is set to a value equal to or less than the atmospheric pressure and set to a value which is necessary for the workpiece to drop by its own weight from the suction head.