A capo device for a stringed musical instrument having a series of strings extending along a fretboard with spaced frets, in which each string passes through an aperture in a capo element which is slidable on the string, each element being such that when held against the fretboard it stops the string on which it is mounted at the adjacent fret. The elements have horse-shoe type magnets which interact with a ferromagnetic fretboard to hold each element against the fretboard at one of a number of selected positions while allowing the element to be moved to a stored position when not in use. The stored position is provided between a string nut and a string guide which contacts the strings between the nut and tuning pegs for the strings, the elements being movable over the nut into the stored position. The fretboard preferably has no magnets.