Infrared spectra of benzene were measured at pressures up to 25.3 GPa at room temperature using a diamond anvil cell. With decompression from pressures above 18.7 GPa, a new peak of C-H vibration mode appeared at a lower frequency than that of benzene. This indicates that an irreversible chemical change occurred at a pressure that was lower than that reported in previous studies. The IR spectra of the recovered sample after compression up to 20.3 GPa are comparable with those of the amorphous hydrogenated carbon reported in the previous study that was formed by compression of benzene up to approximately 30 GPa.