An odd-cylinder V-type internal combustion engine including 2nnull1 cylinders (n is a natural number) arranged in two banks and pistons fitted in the cylinders has a crankshaft provided with n common crankpins (KC) each connected to the two paired pistons respectively belonging to the two banks, and one odd crankpin (KS) connected to the one unpaired piston. The common crankpins (KC) are disposed at the same phase. Bank angle null between the two banks meets nullnullcosnull1(1/2n). The odd crankpin (KS) is disposed (180nullnull)null behind the common crank pins (KC) with respect to the rotating direction of the crankshaft when the unpaired piston belongs to the front bank with respect to the rotating direction of the crankshaft. Reciprocating parts including all the pistons fitted in the cylinders have the same mass (M), and the crankshaft is provided with balance weight means capable of generating a balancing force of kMrnull2 acting in a sense of (nullnull180)null, where: 1 k = ( 1 2 null 1 - 1 4 null n 2 ) 2 + ( n - 1 4 null n ) 2 null = sin - 1 ( 1 2 null 1 - 1 4 null n 2 k ) null: Angle from the common crankpins in the rotating direction M: Mass of each reciprocating part r: Crank throw null: Angular velocity of the crankshaft The odd-cylinder V-type internal combustion engine prevents generation of a primary vibration caused by a primary inertial force without entailing increase in weight and size.