According to one aspect of the invention, a diagnostic apparatus for a fuel cell installed in a moving object as a power source is characterized by comprising an operation control portion that is connected to a control system installed in the moving object to perform operation control of the fuel cell and that performs operation control of the fuel cell by issuing an operational instruction to the control system, a diagnostic portion that diagnoses a state of the fuel cell on the basis of operation of the fuel cell controlled by the operation control portion, and a power adjustment portion that adjusts power obtained from the fuel cell operated by the operation control portion during a diagnosis made by the diagnostic portion.