An object position area detection unit of an object detection device detects a position area of an object included in an inputted image, on the basis of a first class definition in which a plurality of classes are defined in advance. A class identification unit identifies which of the plurality of classes the object belongs to, on the basis of a second class definition in which a plurality of classes are defined in advance. An object detection result output unit outputs an object detection result on the basis of a detection result of the object position area detection unit and an identification result of the class identification unit. The number of classes defined by the second class definition is smaller than the number of classes defined by the first class definition. The plurality of classes defined by the second class definition are formed by collecting some of a plurality of classes defined by the first class definition.