PURPOSE: To prevent any rotatory fluctuation of a propeller from occurring at a time when a temperature of pressure oil being fed to a hydraulic cylinder is low, by releasing a supply of the pressure oil into the hydraulic cylinder of a pitch angle control mechanism when the oil temperature is as low as less than the specified value, and setting the pitch angle of a propeller blade to a minimum angle.

CONSTITUTION: A microcomputer 30 reads oil temperature Toil, engine speed Ne and throttle opening θth from each signal out of three sensors S1, S2, S3, and it judges whether the oil temperature Toil is higher or lower than the specified temperature T. When the oil temperature Toil is lower than the specified one T, desired engine speed Nset of an engine is set to the maximum, and the pitch angle to the minimum angle Lo, respectively, thereby holding a solenoid selector valve 21 in a second position. With this constitution, pressure oil is discharged to a reservoir R from a hydraulic cylinder in propeller hub 11 and thereby the pitch angle of a propeller blade 12 is held to the minimum angle, and the engine speed goes up, thus warming up of the engine takes place.