1. A radar apparatus for use in a vehicle comprising: a transmitting/receiving unit for transmitting a radar wave frequency-modulated so as to linearly vary in frequency with time at every predetermined measurement cycle, receiving the radar wave reflected from a target as a reflected wave, and generating a beat signal by mixing a transmission signal of the radar wave with a reception signal of the reflected wave; a frequency analyzing unit for deriving power spectrum indicative of frequency contained in the beat signal and intensity at each frequency each time the transmitting/receiving means generates the beat signal; a target candidate detecting unit for detecting, as a target candidate which has a possibility of being the target, a peak frequency indicative of each frequency at which the intensity of the power spectrum becomes maximum, and deriving a position and a speed of each target candidate each time the frequency analyzing unit generates the power spectrum; a road shape recognizing unit for sequentially connecting along a predetermined direction and grouping together the target candidates which are detected by the target candidate detecting unit at one or more measurement cycles and which are stationary and present within a set first reference distance from a position of the target candidate making a reference point, and recognizing a road shape including at least a road edge which is an area where positions of the grouped target candidates are connected in the order of connection; an object recognizing unit for making a determination, for each of the moving target candidates which are detected by the target candidate detecting unit, that the target candidate is a moving object if the target candidate detected at the next measurement cycle continues to be within a set second reference distance from a predicted position of the target candidate predicted based on positions of the target candidate detected at previous measurement cycles for over a predetermined number of the measurement cycles; a cruise environment estimating unit for estimating that a cruise environment representing an environment of a road on which an own vehicle is running is a closed space where a space above a running surface of the road is closed if an integral value of the intensity of the power spectrum derived by the frequency analyzing unit for a predetermined frequency range is larger than a predetermined reference threshold value; and a reference distance correcting unit for shortening at least one of the first and second reference distances if the cruise environment is estimated to be the closed space by the cruise environment estimating unit compared to if the cruise environment is an open space.