Soft x-ray emission spectroscopy was used for elucidating the electronic structure of ionic liquids [C4mim]+PF6− and [C4mim]+OTf−, where [C4mim]+ stands for methylbutylimidazolium cation and OTf− for the trifluoromethanesulfonate anion. Nonresonant spectra measured above N, O, and F 1s edges selectively probed the molecular orbitals (MOs) of the cation and anions. They give a clear evidence that the highest occupied molecular orbital of the [C4mim]+ cation contributes to the topmost occupied states of the ionic liquids [C4mim]+PF6−, while both cationic and anionic MOs contribute for the case of [C4mim]+OTf−. Resonant soft x-ray emission spectra at the N 1s edge of these ionic liquids revealed that the energy gap of [C4mim]+PF6− is solely determined by the [C4mim]+ cation, in contrast to usual ionic crystals. The ionic liquids form a new class of the ionic materials from the viewpoint of the electronic structure.