To provide a robot deterioration diagnostic device capable of determining presence/absence of deterioration in a robot driving system even when characteristic data given in refresh operation in the past are different from that given in refresh operation in the present.

This robot deterioration diagnostic device is provided with a data accumulation part reading a group of characteristic data from a robot controller, which records a group of characteristic data as data used for deterioration diagnosis every time when one cycle of the refresh operation is finished in a work program used for deterioration diagnosis, every time when the group of characteristic data are updated, a data analysis part reading the group of characteristic data stored in the data accumulation part and analyzing it by a statistical method, and a deterioration diagnostic part diagnosing a mechanical deterioration symptom of a robot arm based on the analysis result in the data analysis part.