Abstract: In a trim-tilt device for a marine propulsion unit 20, a cylinder 41 of a cylinder device 21 is covered with a tank 28 constituting a hydraulic fluid supply/discharge device 22 and a relief valve 131 is opened when hydraulic pressure of the tank 25 becomes higher than a fixed value, so that hydraulic fluid of the tank 25 can be relieved for the second tilt chamber 32B.

Abstract: In a trim-tilt device for a marine propulsion unit (20), a check valve (121) is provided for allowing a hydraulic fluid to flow from a pump (24) to a first trim chamber (32A) and a first tilt chamber (42A), and a relief valve (122), which is opened if the hydraulic pressure of the first trim chamber (32A) and the hydraulic pressure of the first tilt chamber (42A) become higher than a fixed value, are connect in parallel to a hydraulic fluid low passage (91) connecting a first trim chamber (32A) and a first tilt chamber (42A) to a pump (24).

Abstract: A tilt cylinder for tilting an outboard engine has first and second cylinder chambers. A pair of on/off valves is movably disposed in respective fluid passages connected to a hydraulic pump and the first and second cylinder chambers, respectively. The on/off valves are operatively combined with respective shuttle valves which have respective oil passages in facing relationship to the on/off valves, respectively, and respective ball valve bodies for selectively opening the oil passage into communication with each other. When the hydraulic pump is actuated to develop a working oil pressure buildup, one of the on/off valves is opened by the working oil pressure buildup to establish an oil supply passage from the hydraulic pump to one of the first and second chambers, and the other of the on/off valves is opened by the coacting shuttle valve which is moved by the working oil pressure buildup to establish an oil return passage from the other of the first and second chambers to the hydraulic pump.