PURPOSE: To reduce the size and provide ready assembly by placing a tilt cylinder inside a storage cavity which is integrally molded with a cramp bracket and by making the axis of the tilt cylinder substantially perpendicular to a swivel bracket.

CONSTITUTION: A swivel bracket 14 is held by a cramp bracket 13 which is fixed to a stern board 12 of a hull 11 so that the bracket 14 can be rotated on the substantially horizontal axis. A thrust unit 15 is supported so that the unit can be rotated on the substantially vertical axis. A closing member 21 is closely fit at the interior side to a storage cavity 20 which is integrally molded with a cramp bracket 13. A tilt cylinder 26 is secured inside the storage cavity 20 with a pin and connected to the swivel bracket 14. A pump unit 30 is disposed inside the hull and connected to the tilt cylinder 26 by a fluid pipe 31.