To suppress deviation of a transmitting velocity ratio between in a normal state and in an inverted state, in a V-ribbed belt including plural cross-sectionally nearly trapezoidal rib parts respectively extending in the longitudinal direction of the belt parallel to each other on its bottom face and back face.

A difference between a bottom face side belt length when a bottom face side rib parts 3 of this belt B are located on the belt inner circumferential side and a back face side belt length when a back face side rib parts 4 are located on the belt inner circumferential side is set to 2 mm or less, while a center position of each core wire 2 within the belt B is disposed in a nearly central part of a belt thickness. Thereby, intervals of the core wires 2 from the belt bottom face and back face are equal whether the belt B has a normal state or an inverted state.