With a two-crystal vacuum spectrometer, the Cl - K α emission spectra in fluorescence are measured for a series of alkali chlorides MCl (M=Li, Na, K, Rb and Cs). By using the measured K α emission spectra, the previously reported Cl - K β emission spectra, ultraviolet photoelectron spectra, and optical-gap data, the energy position of the bottom of the conduction band is shown in the high-resolution Cl - L 2,3 absorption spectra of alkali chlorides obtained by Iguchi et al . The first sharp peak of the Cl - L 2,3 absorption is identified as being due to a core exciton, the energy level of which is formed below the bottom. The binding energies of the excitons are estimated to be 0.9 (±0.1), 1.2 (±0.1), 1.3 (±0.1), 1.1 (±0.1) and 0.7 (±0.1) eV for LiCl, NaCl, KCl, RbCl and CsCl, respectively.