To suppress rotational variation of a crankshaft and other auxiliary machines when an electric power generation amount of an alternator varies.

An internal combustion engine comprises: an alternator pulley 3 provided at one side across a crankshaft, for transmitting rotational driving force to an alternator; auxiliary machine pulleys 5, 6 and an idler pulley 4 provided at the other side, for transmitting rotational driving force to auxiliary machines of the types other than the alternator; and a tensioner 2 provided above the crankshaft, for adjusting tension of a wrapping transmission member 7, wherein the wrapping transmission member 7 is configured to be wrapped in order of at least the tensioner 2, the alternator pulley 3, and the idler pulley 4. The idler pulley 4 is disposed at a position higher than the alternator pulley 3 and the auxiliary machine pulleys 5, 6.