On a main line, when an empty space equal to or greater than a predetermined length is detected between lots of articles or between articles being conveyed, this detected empty space is reserved for an article arrival line on which articles are stored. Static and dynamic configuration data is stored in flash memory. The ion current detecting electrode portion 14 is constructed, at its portion including at least a portion of the ion current detecting face 15, of a conductive ceramic phase which is composed mainly of non-metallic conductive ceramic having a cation component made of a nonmetallic element, such as silicon carbide.