We analytically show that mesonic bound states of confined monopoles appear inside a non-Abelian vortex-string in massless three-flavor QCD at large quark chemical potential mu. The orientational modes CP^2 in the internal space of a vortex is described by the low-energy effective world-sheet theory. Mesons of confined monopoles are dynamically generated as bound states of kinks by the quantum effects in the effective theory. The mass of monopoles is shown to be an exponentially soft scale Delta*exp[-c*(mu/Delta)^2], with the color superconducting gap Delta and some constant c. A possible quark-monopole duality between the hadron phase and the color superconducting phase is also discussed.