A disposable automobile seat cover having a cover portion to enclose a portion of an automobile seat and an elastic band around the perimeter of the cover portion. The rack has a pair of lateral rails for holding the carrier. The distribution control unit mixedly distributes the two kinds of the boards to each of the first and second board conveyance mechanisms based on a board request signal issued from a most-upstream component mounting unit in the component mounting line. At each moved position, scanning is performed on a given pulse sequence.