A parallel running vehicle detecting apparatus is provided, which includes a first distance sensor for detecting distance of an object in a first detection area on a rear lateral side of a vehicle, a second distance sensor for detecting distance of an object in a second detection area, a parallel running vehicle detector for detecting a parallel running vehicle based on detections of the first and second distance sensors, and a storage for storing a detection distance history of the second distance sensor. The parallel running vehicle detector is provided with multiple determination conditions for determining whether the object detected by the first distance sensor is the parallel running vehicle, and changes the parallel running vehicle determination condition based on the detection distance history stored in the storage.