A memory system permitting a number of alternative memory blocks to be made ready in order to extend the rewritable life and thereby contributing to enhanced reliability of information storage is to be provided. Within a particular switch, a particular combination of pending OPN conditions is detected, indicating a lockup condition. Each one of the windows comprises two axes. Next, third discharge is caused by applying positive rectangular waveform voltage to the scan electrode. The tubular element and the tube comprise means preventing the tubular element from being separated from the tube after one has been mounted into the other.