The invention relates to a device for altering the tension of the strings of a stringed musical instrument, of the type comprising a structural element, with at least one element for securing to the body of the instrument, said structural element comprising at least two runners each secured to at least one string of the instrument, and an actuation mechanism for actuating the runners in order to alter the tension of the strings of the instrument, comprising at least one slide carriage that can be moved by the action of at least one lever.