To provide a torsional vibration stress reduction control device for reducing torsional vibration stress by simple control.

A torsional vibration stress reduction control device 50 is configured to reduce torsional vibration stress generated in a propulsion shafting 10 in a marine vessel 100 including a propulsion shafting 10 which rotates integrally with a propulsion propeller 11, a main engine 20 for driving the propulsion shafting 10, and a supercharger 30 which has a turbine 31 driven by exhaust 27 expelled from the main engine 20 and which uses the rotational force of the turbine 31 as motive power to compress new air and supply scavenged air 24 to the main engine 20. The pressure of the scavenged air 24 is reduced when the torsional vibration stress is a predetermined value or greater.