The present invention is an apparatus which enables a harmonica to be removably attached to a string instrument such as a guitar without having to modify the physical aspects of the guitar and which retains the harmonica so that it can be immediately located and grasped into a playing condition so that a musician can play the guitar or other string instrument, immediately switch to playing the harmonica, and then return the harmonica to its location on the guitar and continue to play the guitar. More broadly defined, the present invention includes the concept of removably retaining a first musical instrument to a second musical instrument by a magnet.