A diagnosis device includes: an obtainer that obtains operation data about equipment; an identifier that identifies a reproduction model using the operation data obtained by the obtainer; a reproduction data generator that generates reproduction data about the equipment based on the reproduction model identified by the identifier; a diagnosis model generator that performs machine learning using the reproduction data generated by the reproduction data generator, to generate a diagnosis model of the equipment; a diagnoser that diagnoses the equipment based on the diagnosis model generated by the diagnosis model generator; and a display that is an example of an outputter for outputting a diagnosis result provided by the diagnoser.