According to one embodiment, a conveyor diagnostic device diagnoses an abnormal state of a cyclically moving conveyor. The conveyor diagnostic device includes a first tilt sensor, a second tilt sensor, a table, and a processing unit. The first and second tilt sensors are attached to a predetermined position of the conveyor and detect tilt angles of the conveyor in a vertical direction and horizontal direction, respectively. The table indicates a relationship between a tilt angle which changes in the vertical direction and sections included in one revolution of the conveyor. The processing unit specifies an abnormality occurrence position of the conveyor based on a tilt angle in the vertical direction, the table, and an elapsed time after ingression for a section corresponding to the tilt angle in the vertical direction, when a tilt angle in the horizontal direction exceeds a predetermined management limit value.