A battery separator is provided which is hardly broken by tension during the manufacture of batteries, is hardly punctured with a plate flash, and is hardly torn off with a plate edge, thereby hardly causing a short circuit. Triggered by detection of its leading end at a second sensor, an opposite-direction separation force is applied to the sheet to be conveyed via the separation roller. The algorithm mathematically determines, based on the measured changes in capacity of the wireless data link, optimum locations at which, when the mobile vehicles are positioned there, the capacity of the wireless data link reaches a local maximum value. The side walls have side edge portions bonded to the vicinity of transversely opposite side edges of the core and first end portions bonded to the end flaps. A control unit controls ejection of ink from the print head of the first carriage based on an output from the first position detector, and ejection of ink from the print head of the second carriage based on the output from the second position detector.