There are provided a processor device for an endoscope capable of acquiring a blood vessel index value of a specific observation distance used for predetermined diagnostic criteria, an operation method thereof, and a control program. A distance acquisition unit (72) acquires a non-magnified observation distance L1 at the start of the change of the imaging magnification, and acquires magnified observation distance L2 at the end of the change of the imaging magnification. A distance ratio calculation unit (74) calculates a first distance ratio D between the non-magnified observation distance L1 and the magnified observation distance L2. A blood vessel index value calculation unit (76) calculates a blood vessel index value of the non-magnified observation distance L1 from the image signal acquired at the non-magnified observation distance L1. An index value correction unit (78) corrects the blood vessel index value of the non-magnified observation distance L1 according to the first distance ratio D to acquire a blood vessel index value of the magnified observation distance L2.
