A public graphic library coupled to a WAN offers access to a database of graphics, while another graphic library inside the firewall of an enterprise network provides graphics to users in an enterprise. The shots are fired in a sequence and pattern such that no laser shots are fired at consecutive locations and no consecutive shots overlap. When the estimated heat generation value reaches a preset stopping point or when a thermostat attached to the drive section outputs an overload detection signal indicating an overload state, the drive motor is stopped. The product RA resistance x area of the two tunnel barriers is different.