A device for transforming alternating rectilinear motion into intermittent rotary motion, in particular for the command of indexed rotary tables. The device includes at least one fixed base element (11) with cam guide elements (14), a moving slide element (12) associated with the fixed element, equipped with mechanical locator elements (15) following the cam guide elements (14) and susceptible to alternating movements on and with respect to the fixed base element commanded by an actuator, and an index plate (13) rotatably associated with the fixed element, interacting mechanically with the moving slide element (12) and susceptible to angular rotation pitch in answer to the alternating movements of the moving slide element. The index plate is connected to an indexed rotary table to be commanded.