9 a the engine 2 drives the drive shaft 7 to drive the propeller 9 via the transmission mechanism 8 thereby to provide the outboard motor 1 with a propulsion power a covering means 10 constituting a part of the shell member of the outboard motor 1 covers upper side and lower portions of the engine 2 the covering means 10 consists of a cover structure having a first cover member comprised of a cap shaped engine cover 11 oriented downward for covering an upper portion of the engine 2 above a vertically intermediate portion thereof and a second cover member comprised of an undercover 20 for enclosing a lower portion of the engine 2 the pump body 3 the mounting case 4 and the oil case 5 the undercover 20 as shown in fig3 consists of two cover portions a left lower cover 21 and a right lower cover 31 as left and right cover members the engine space 12 is defined by the engine cover 11 and an upper portion of the undercover 20 in other words the engine space 12 is formed by an upper portion separated from a lower portion by the mounting case 4 as will be described below the engine space 12 is located.