PURPOSE: To enables a piston to be firstly lowered to separate a trim rod from a bracket even if the bracket makes contact with the trim rod, by a method wherein a down motion on the trim cylinder side is increased over that on the tilt cylinder side.

CONSTITUTION: When a liquid pressure pump 9 feeds liquid by a pressure to a passage 10 through a passage 11 by means of down motion, a liquid pressure in a trim cylinder upper chamber 7e is lower by a specified pressure P1 than a pump pressure with the aid of a pressure reducing valve 22 located to a flow pass 21 running to the trim cylinder upper chamber 7e, and a liquid pressure in a tilt cylinder upper chamber 6b is lower by a specified pressure P2 with the aid to a valve 12f. If the specified pressures are set to P1>P2, the depressing force of a tilt piston 6c is increased over that of a trim piston 7d, the tilt side is firstly lowered, and even if a down bracket makes contact with a trim cylinder, the trim piston is prevented from being separated from the bracket.