1. An object detection apparatus comprising: a storage storing, for each of a plurality of part areas forming an area in an input image that is subject to image recognition processing and is referred to as a subject area, image recognition dictionaries that are used to recognize a target object to be detected in the input image and are typed according to variations in appearance of a part of the target object to be detected in the part area; a part score calculator configured to calculate, for each of the part areas forming the subject area cut from the input image, a part score indicative of a degree of similarity between the part area and each of at least some of the image recognition dictionaries stored in the storage; an integrated score calculator configured to calculate an integrated score by selecting, for each of the part areas forming the subject area, one of the scores calculated in the part score calculator and then calculating a weighted sum of the selected part scores for the respective part areas of the subject area; and a determiner configured to determine, on the basis of the integrated score calculated in the integrated score calculator, whether or not the target object is present in the subject area; wherein the integrated score calculator is configured to adjust the integrated score by variably setting weighting factors used to calculate the weighted sum of the selected part scores as a function of a combination of the image recognition dictionaries involved in the calculation of the integrated score.