According to an aspect of the invention, a diagnostic apparatus which diagnoses a state of the fuel cell includes an operation device which is used for operating the fuel cell; an operational state detecting portion which detects a change in an operational state of the fuel cell; a device control portion which controls the operation device such that the fuel cell is operated according to at least one predetermined operation pattern; and a diagnostic portion which diagnoses the state of the fuel cell based on the change in the operational state of the fuel cell that is detected by the change in the operational state detecting portion when the fuel cell is operated by the device control portion according to the at least one predetermined operation pattern, and the at least one predetermined operation pattern.