A vehicle-installed direction detection apparatus is controlled in accordance with the vehicle speed, to detect respective directions of one or more target objects by selectively applying high-resolution detection processing or low-resolution detection processing to received signals obtained from the elements of an array antenna of a radar apparatus, with the selection being determined in accordance with whether the speed attains a predetermined threshold value. The high-resolution detection processing is based on correlation between the received signals, utilizing an null scan type of algorithm such as MUSIC, while the low-resolution detection processing is based for example on digital beam forming.