A failure diagnostic device comprising: a torque detection part that detects disturbance torques (Tq) applied to joint shafts included in a multi-axis robot ; a torque grouping circuit that groups the disturbance torques (Tq) according to a content of an operation executed by the multi-axis robot upon detection of each disturbance torque (Tq); characterized by : a torque correction circuit that obtains, for each group of disturbance torques (Tq), a corrected disturbance torque (Tq') standardized between a plurality of operations with different contents, on a basis of a difference between each of the disturbance torques (Tq) detected by the torque detection part and a representative value of the disturbance torque (Tq) detected during the operation executed by the multi-axis robot for each grouped disturbance torque, wherein the representative value is preliminary set for each group of disturbance torques (Tq); and a failure diagnostic circuit that performs a failure diagnosis on the multi-axis robot by comparing each of the corrected disturbance torques (Tq') obtained for the operations with different contents, with a common threshold (α) regardless of the contents of the operations. a torque detection part that detects disturbance torques (Tq) applied to joint shafts included in a multi-axis robot ; a torque grouping circuit that groups the disturbance torques (Tq) according to a content of an operation executed by the multi-axis robot upon detection of each disturbance torque (Tq); characterized by : a torque correction circuit that obtains, for each group of disturbance torques (Tq), a corrected disturbance torque (Tq') standardized between a plurality of operations with different contents, on a basis of a difference between each of the disturbance torques (Tq) detected by the torque detection part and a representative value of the disturbance torque (Tq) detected during the operation executed by the multi-axis robot for each grouped disturbance torque, wherein the representative value is preliminary set for each group of disturbance torques (Tq); and a failure diagnostic circuit that performs a failure diagnosis on the multi-axis robot by comparing each of the corrected disturbance torques (Tq') obtained for the operations with different contents, with a common threshold (α) regardless of the contents of the operations. a torque correction circuit that obtains, for each group of disturbance torques (Tq), a corrected disturbance torque (Tq') standardized between a plurality of operations with different contents, on a basis of a difference between each of the disturbance torques (Tq) detected by the torque detection part and a representative value of the disturbance torque (Tq) detected during the operation executed by the multi-axis robot for each grouped disturbance torque, wherein the representative value is preliminary set for each group of disturbance torques (Tq); and a failure diagnostic circuit that performs a failure diagnosis on the multi-axis robot by comparing each of the corrected disturbance torques (Tq') obtained for the operations with different contents, with a common threshold (α) regardless of the contents of the operations. <EOS>