The structure of species formed in $NbCI_5-I-ethyl-3-methylimidazolium$ chloride (EMIC) room-temperature molten salt (RTMS) was examined with the Raman spectroscopic measurement and ab initio molecular orbital calculation. The equilibrium structures of $NbCl_5,;NbCl_6^-,;Nb_2CI_{10},;Nb_2CI_{11}^-,;Nb_3CI_6^-,;NbCI_6^--EMI^+;(in;which;NbCI_6^-$ anion approaches $EMI^+$ cation with strong interaction) and $Nb_2CI_{11}^--EMI^+$ were obtained with the HF/LANL2DZ level of calculation. The harmonic frequencies at each equilibrium structure were compared with Raman spectra. The harmonic frequencies of $NbCI_6^--EMI^+,; Nb_2CI_{11}^--EMI^+,;and;Nb_2CI_{10}$ were in good agreement with the Raman spectra of RTMS melts. In the $NbCI_5-EMIC RTMS$, the main species were $NbCI_6^-;and;EMI^+$. In the $NbCl_5-EMIC$ RTMS added $NbCl_5;over;50mol\%$, small amount of $Nb_2CI_{11}^-;and; Nb_2CI_{10}$ were also formed. The structures of anions and cation in the RTMS distorted from free ions with Coulomb force.