To provide a drive system diagnostic device capable of efficiently diagnosing operation of a drive system having an actuator and a transmitting mechanism for transmitting the power of the actuator.

A theoretical value acquiring means 101 acquires a theoretical value of drive speed by the drive system. An actual measurement acquiring means 102 acquires an actual measurement of the drive speed of the drive system based on motion of a transmitting function. A diagnostic means 103 diagnoses the operation of the drive system by comparing the theoretical value acquired by the theoretical value acquiring means 101 with the actual measurement acquired by the actual measurement acquiring means 102. An alarm informing means 104 informs an alarm in accordance with the diagnosis result by the diagnostic means 103.