PURPOSE: To prevent emergency shutdown and breakage of a device during electronic part mounting operation caused by false data input by judging that false data input to a control device exists regarding a movement amount of a mounting head which is necessary for unloading of a part when a sensor detects a mounting head.

CONSTITUTION: Movement amount data of a mounting head 30 is input to a control device for each of electronic part supply units 22a, 22b, .... Thereafter, the mounting head 30 is moved at a low speed by a longest distance in Y- direction which is required for unloading a part. An OT sensor 40 continues to monitor whether or not the mounting head 30 enters inside a monitor line 40a until the mounting head 30 attains a final end of movement. When the mounting head 30 screens the monitor line 40a, detection of the mounting head is output to a control device. The control device whereto the detection signal is input commands a driving part of the mounting head 30 to stop movement for emergency stop of movement of the mounting head 30. Simultaneously, the control device informs an operator of an error.