A mechanism for tilting an outboard motor. The mechanism has an outboard motor which is attached to a hull so as to be tilted up and down, a cylinder for driving the outboard motor to change a posture of the outboard motor, and a linkage to connect the outboard motor and a rod of the cylinder. The cylinder itself serves as a central shaft, around which the outboard motor is tilted up and down. Since the cylinder has a single-walled construction, the mechanism of the present invention is simple and can be economically manufactured.