CRANKCASE OF INTERNAL COMBUSTION ENGINE

To provide a crankcase of an internal combustion engine which can prevent the generation of sounds from a protruding portion of the crankcase and can be light-weighted. Protruding portions (212) which are formed on an outer surface of a crankcase (3) are constituted of a pair of left and right wall members (212A, 212B), and a vibration isolating rubber (301) is fitted between the wall members (212A, 212B).