A system andor method for increasing safety in areas in which people work andor through which people travel that potentially may become blocked is provided. A driving roller, a tensioning roller and a supporting member are supported to a frame so as to be movable in upward and downward directions, and a portion spacing mechanism moving an elevating rod in upward and downward directions by rotation of a motor is provided. In addition a positioning marking is also printed on the printing substrate web in a predetermined position relative to the print marking in order to determine a relative position between the print marking and the measurement region of the color measurement unit. A width of response of the amplifier is tuned by varying the pump voltage. Further, since the size of the file to be transferred can be predetermined, and since any retransmissions can be made over a path other than the circuit, the circuit that best meets the needs of the data transfer can be selected, thereby further increasing the efficiency with which the circuit is used.