In the state that a preceding sheet awaits at an awaiting position, a pair of conveying rollers are separated from each other, and the front end of a subsequent sheet sent out from a main conveying path passes the gap between the pair of conveying rollers. In testing each identified control for an associated label, an accessibility interface query can be applied to each identified control in the window. The invention also includes shock means for applying a sudden force to the first blade. The insulating members are pressed in the gas discharge holes to bring the steps into contact with shoulders formed in the sidewalls of the gas discharge holes.