In an object detection apparatus, a first region definition unit defines a first object region including a first detection point representing a relative position of a first object detected based on detection information from the radar. A second region definition unit defines a second object region including a second detection point representing a relative position of a second object detected based on a captured image from a monocular camera. A learning status acquisition unit acquires a learning progress status to estimate a position of FOE on the captured image. If there is an overlap of the first and second object regions, a determination unit determines that these objects are the same object. The second region definition unit sets a length of the second object region in a depthwise or vehicle-lengthwise direction representing a direction of the second detection point with respect to the reference point depending on the learning progress status.