PURPOSE: To facilitate assembly/disassembly by providing a driving shaft housing which extends so as to support a propeller and be capable of inserting and withdrawing a camshaft through a camshaft aperture in the bottom wall portion of a cylinder head.

CONSTITUTION: This outboard motor 11 involves a lower unit 13. The lower unit 13 has a driving housing 15 which supports a propeller 29, is fixed to a cylinder block lower mounting surface 35, and has an upper and rearward profile located ahead of the opening in the camshaft 77, and extends so as to be capable of inserting and withdrawing the camshaft 77 through the opening in the camshaft 77 in the bottom wall portion of the cylinder head when the housing 15 is fixed to the cylinder block 35. It is thus possible to facilitate removal of the camshaft 77 or rocker arm supporting shaft for inspection, replacement, or other reason.