An electronic mail wrong transmission determination apparatus includes: a feature information creation unit which creates feature information related to contents of an electronic mail that is a transmission object; an accumulation unit which accumulates feature information related to contents of a transmitted electronic mail and a destination of the transmitted electronic mail in association with each other; a destination candidate selection unit which selects destination candidates that are similar in appearance to a destination of the electronic mail that is the transmission object, from destinations of transmitted electronic mails; a similarity model creation unit which creates a similarity model for each destination accumulated in the accumulation unit based on the feature information accumulated in the accumulation unit in association with the destination and based on the feature information accumulated in the accumulation unit in association with other destinations that differ from the destination; wherein the similarity model serves as a criterion of determination as to whether or not feature information related to contents of an arbitrary electronic mail belongs to a certain feature information region in the word space, which is defined according to the contents of the electronic mails transmitted to the destination so far; and a reliability calculation unit which calculates respective reliabilities of a destination and destination candidates of the electronic mail that is the transmission object, based on feature information related to contents of the electronic mail that is the transmission object, based on the similarity model related to the destination of the electronic mail that is the transmission object, and based on the similarity models related to the destination candidates.