An ECU recognizes an object detected by a radar sensor and an object detected by a camera sensor as the same object on condition that there is an overlapping region between a reflected wave search region and an image search region. The ECU determines the brightness in the direction in which the object is detected by the camera sensor in response to recognizing the object detected by the radar sensor and the object detected by the camera sensor as the same object. The ECU then changes the size of the image search region based on the determined brightness in the direction in which the object is detected.