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Until now, a large number of studies on the microscopic solvation effect of metal ion have been carried out. However, a very small number of spectroscopic studies on the doubly-charged metal ions are reported compared with that on the singly-charged ion. Since doubly-charged metal ions are highly energetic, electron- or proton- transfer reactions with solvent molecules should compete with the stabilization by solvation. Thus, we have carried out infrared spectroscopy of the hydrated doubly-charged metal ions. \par In the present study, we used the electrospray ionization method to produce the hydrated doubly-charged metal ions. The ions mass-separated by the first quadrupole mass filter are irradiated by IR laser light and then fragment ions are detected by the second quadrupole mass analyzer. In the case of Mg$\mathrm{<mrow\; data-mjx-texclass="ORD">2+</mrow>}$(H$2$O)$7$, a structure where one water molecule is hydrogen-bonded to the 6-coordinated Mg$\mathrm{<mrow\; data-mjx-texclass="ORD">2+</mrow>}$ is indicated by the IR spectrum. IR spectra of other systems will be presented in the paper. \par