PROBLEM TO BE SOLVED: To provide a field bus communication diagnostic device and a field bus communication diagnostic method for accurately diagnosing the failure of field bus communication without imposing a burden on an operator. SOLUTION: A communication status storage means 21 stores the communication error status of field bus communication. A connection status updating means 22 updates connection status about the field bus communication of two systems. A diagnostic means 23 successively acquires communication error status stored in the communication status storage means 21 in a fixed period, and diagnoses the communication state of field bus communication based on the acquired communication error status, and successively acquires the connection status updated by the connection status updating means 22 in the fixed period, and diagnoses the communication state of the field bus communication based on the acquired connection status. COPYRIGHT: (C)2008,JPO&INPIT
