In the reduction gears for marine propulsion engine such as turbine or high speed diesel engine, the standard involute double helical gears are generally used. However the addendum modification gear can be used in the reduction gear as it has flexibility for gear design on the tooth strength, scoring and operating noise. In this case, the determination of gear shaft bearing load is difficult by the alternation of operating pressure angle. In this paper, the formulas of bearing load according to the arrangements of the reduction gears are derived and the diagrams of operating pressure angle according to the modification coefficient are presented.