The frame of data that is decoded is one of a set of frames that represent a packet of information words, and that additionally represent coded control words preceding and following the packet. The suction device 1 includes a cylinder holding tubular body 1a provided with a single passage 2 and left and right branch passages 2a and 2b bifurcated from the single passage 2 for connecting to a suction apparatus such as a vacuum pump. Adjacent ends respectively of a pair of elastic cords adjacent to each other are securely held by an associated handle. The aperture stop provides a large depth of focus and enables symbols to be read over a wide field of view.