1. A vehicle rear left and right side warning apparatus, comprising: a three-dimensional object detecting unit that detects, by using a pattern recognition technology, a three-dimensional object that exists at rear left and right sides of a vehicle, with respect to images captured by cameras that photograph the rear left and right sides of the vehicle; a warning issuing unit that issues a warning when a relative positional relationship between the vehicle and the three-dimensional object detected by the three-dimensional object detecting unit satisfies a predetermined condition; a driving-lane detecting unit that detects a driving lane of the vehicle; and a recognition-priority setting unit that varies and sets a recognition priority for a type of three-dimensional object that the three-dimensional object detecting unit detects by using the pattern recognition technology, based on the driving lane detected by the driving-lane detecting unit and whether a three-dimensional object is detected at the rear left side or at the rear right side of the vehicle; wherein the recognition priority includes a first recognition priority and a second, lower recognition priority, and wherein a condition for recognizing that a detected three-dimensional object matches a type of three-dimensional object is tightened for the second recognition priority relative to the first recognition priority to reduce false recognitions.