To allow the change of both ranges of the set values of propeller rotating speed control and slip factor control in a hydraulic control mechanism for a marine reduction reversing gear fixed to the rear part of an engine to change the rotation of a propeller for a ship ahead and astern to change speed.

In constitution allowing control for making propeller rotating speed constant in the marine reduction reversing gear provided with a means for increasing/decreasing the operating oil pressure of a hydraulic clutch, the range of a trawling dial 11 for setting the propeller rotating speed is changeable.