A system includes a transmission unit, a reception unit, and a lens unit and is placed in a passage, wherein in a case where a first plane that intersects a forward direction of the passage and is a surface of an object, and a second plane that intersects the forward direction of the passage, includes the lens unit, and is at a position different from a position of the first plane are set, a first area to which a terahertz wave from the transmission unit reflected from the first plane is emitted and the lens unit are disposed at positions different from each other on the second plane.