1. An object detection apparatus, comprising: a characteristic information extractor that extracts characteristic information of at least one moving object shown in a photographic image; a reader that reads an identifier of a radio terminal held by the moving object; a history manager that stores the characteristic information and the identifier associated on a time-by-time basis; and an associator that mutually associates the characteristic information and the identifier stored in the history manager based on similarity of the characteristic information and an association between the characteristic information and the identifier, wherein the associator: when a number of identifiers corresponding to a subset to which specified characteristic information belongs is one, mutually associates the specified characteristic information and the identifier; and when a plurality of identifiers exist that are associated with the subset to which the specified characteristic information belongs, extracts characteristic information whose similarity to the specified characteristic information is highest from other characteristic information stored in the history manager, and identifies an identifier corresponding to the specified characteristic information by finding an identifier common to the specified characteristic information and the extracted characteristic information.