FIG. 4A is an external front view of this interrogator 1, FIG. 4B is a sectional view thereof taken along line A-A??? shown in FIG. 4A. and FIG. 4C is a sectional view thereof taken along line B-B??? shown in FIG. 4A. The internal circuits 10 other than the antenna 14 are enclosed in a shielding member 300 made of a material that shuts off, reflects, or absorbs radio waves.