A control device including a failure diagnosis unit configured to identify a phenomenon that is a cause of the detected error, wherein the failure diagnosis unit is configured to: calculate a diagnosable time available to be spent on the identification of the phenomenon that is the cause of the error; and identify, for each detected error, a phenomenon that is the cause of the error based on a posterior probability, which is calculated for each phenomenon that is likely to be the cause of the error as a probability of occurrence of the phenomenon, on a diagnosis time, which is obtained for each phenomenon as a period of time required to identify the phenomenon as the cause of the error, and on the diagnosable time.