The present invention relates to a work head with bead breaker roller for a tire mounting-demounting machine, suitable for bead breaking of a tire (P) from the edge (B1) of a rim (C) of a tired wheel, the work head comprising: - a head-holder support (10) fixable to a bead breaker arm of a tire mounting-demounting machine; - at least one bracket member (6) pivoted at one end thereof to the head-holder support (10) around a pivoting axis (x-x); - a bead breaker tool (2) supported at the other end of the at least one bracket member (6) and designed to engage a bead of a tire to be bead broken (P); - a lever element (7), which is pivoted to the head-holder support (10) and bears a feeler pin arm portion (9) designed to control, in use, the lever element (7), whereby it is angularly moved between a work position, in which it thrusts against the bead breaker tool, and at least one rest position, it which it is angularly arranged at a distance from the bead breaker tool (2); and - return means (10) designed to yieldably keep the lever element (7) in the work position.