PURPOSE: To automatically control an inclination of a machine propulsion apparatus responding to various states by providing a control means for rotating a propulsion unit around an oblique shaft, and using a water pressure created by relative movement between a boat and water when its hydraulic assembly is pressurized.

CONSTITUTION: A trim control means 30 provided at a marine apparatus 10 is engaged at one end with a boat 18, and engaged at the other end with a hydraulic assembly 32 pressurized by a propulsion unit 22. The assembly 32 has a cylinder 34 and a piston 36, and the means 30 has a means utilizing a water pressure created by relative movement between the boat and a body of water to pressurize the assembly 32, that is, a compressing means 50. Its conduit 52 has a lower end 54 communicating with the water, and its upper end 56 communicates with a chamber 38. When a speed of the board is accelerated, a pressure in the cylinder chamber 38 is pressurized, the piston 36 is pressed, and the unit 22 is rotated to separate a stern beam from a trim-out position.