An object detection apparatus includes means for acquiring image data from an in-vehicle imaging device and means for extracting, from the image data acquired by the acquiring means, an object region which is an image region where a preset object exists. Moreover, the extracting means includes means for identifying the object region, means for measuring the processing time of the identifying means and controlling means. The identifying means includes a plurality of identifiers for identifying candidate regions for the object region. The identifiers are serially linked so as to sequentially refine the candidate regions. The controlling means controls, based on the measured processing time at a preset time point, a degree of refining the candidate regions by the identifying means after the preset time point by adjusting at least one of the linkage between the identifiers and processes to be executed by the identifiers after the preset time point.