In apparatuses and methods for adjusting a distance to an object, or examining an object, by using terahertz radiation, a sensor portion and a distance changing portion are used. The sensor portion includes a generator for generating terahertz radiation, a transmission line for transmitting the terahertz radiation, and a detector for detecting the terahertz radiation transmitted through the transmission line. The distance changing portion is configured to change the distance between the object and the sensor portion. The distance is adjusted based on information of the terahertz radiation detected by the detector. The object is examined based on the information of the terahertz radiation detected by the detector, after the distance is adjusted based on the information of the terahertz radiation detected by the detector. Under a condition of the adjusted distance, leaking electromagnetic field of the terahertz radiation transmitted through the transmission line interacts with the object.