To provide a pivoting arm which prevents a foreign matter from being meshed with a tension pulley in a belt tensioner for an internal combustion engine.

A pivoting arm type belt tensioner has a pivoting arm 38 pivoted by a pivoting member 42 secured to an internal combustion engine at one end and a tension pulley 40 rotatably supported at the other end of the pivoting arm 38, wherein the tension pulley 40 is pressed onto a belt so that the pivoting arm 38 is biased. The pivoting arm 38 has a portion which includes an upper rib 38B and a lower rib part 38C and forms a U-shaped cross section opened toward an internal combustion engine. An upper surface of the lower rib part 38C is tilted so that one end side is lower than the other end side, and is tilted to be lower as it goes toward the internal combustion engine.