A failure diagnosis method diagnoses a failure occurring in a diagnosis target apparatus including a drive mechanism having a drive member that receives power supply to operate and a power transmission member that transmits drive force of the drive member to another member. The method includes automatically acquiring by a sensor an operation state signal indicating an operation state during the drive mechanism operating for a predetermined period; and analyzing the automatically acquired operation state signal based on a failure probability model, which is obtained by modeling a cause of failure occurring in the diagnosis target apparatus with using probabilities, to execute failure diagnosis with respect to each of constituent members of the drive mechanism.