To eliminate some disadvantages in an automatic machine in which when a malfunction of a pressure sensor for discriminating a sucked state of a workpiece occurs, a conveying state is kept stopped for a while even when the sucking section keeps sucked state of a workpiece or all the workpieces are completely conveyed even when no workpiece is sucked.

At first, a sucking section 2 descends to a workpiece installing position, a sucking action (a vacuum operation) is carried out by a source of vacuum, a sucked state is discriminated by a pressure sensor 3. After the pressure sensor 3 discriminates that no workpiece is present, the sucking operation is stopped and the sucking section 2 rises. Then, after the sucking section 2 is moved onto a check plate 4, the sucking section descends so as to suck a check plate 4. At this time, when the pressure sensor 3 determines that there is a workpiece, i.e., the workpiece is sucked against the sucking section 2, the sensor is in its normal state and it can be determined that no workpiece 1 is present at the workpiece mounting position, the sensor is in its normal state and so it becomes necessary to adjust a threshold value of the sensor or perform a maintenance.