1. An image recognition device comprising: a database in which pieces of feature data of a plurality of objects are registered while divided into classes for each of the plurality of objects; an identification unit that identifies an unknown object by evaluating which feature data of the class registered in the database is most similar to feature data obtained from an image of the unknown object; and a feature data registration unit that registers feature data in the database, wherein the database is capable of setting a plurality of classes to an identical object, and the feature data registration unit, in adding new feature data with respect to a first object already registered in the database, sets a new class other than an existing class with respect to the first object, and registers the new feature data in the new class, when a second object satisfying a predetermined similar condition with the new feature data exists in the database.