  An intuitive approach to the glueball using the flux-tube ring solution in
the dual Ginzburg-Landau theory is presented. The description of the flux-tube
ring as the relativistic closed string with the effective string tension
enables us to write the hamiltonian of the flux-tube ring using the Nambu-Goto
action. Analyzing the Schr\"odinger equation, we discuss the mass spectrum and
the wave function of the glueball. The lowest glueball state is found to have
the mass $M_G \sim 1.6 GeV$ and the size $R_G \sim 0.5 fm$.
