In this study, changes of the absolute threshold of hearing were measured by presenting a previous sound in the contralateral or ipsilateral ear. The sound pressure level (SPL) of a previous sound was 40, 60, or 80 dB to investigate the dependence of the threshold change on the SPL of a previous sound. The previous and test sounds were pure tones at the same frequency of 500 Hz and had a duration of 3 s. The previous sound was presented 0.5 s before presenting the test sound. The threshold changes were obtained by subtracting the threshold with a previous sound from the threshold without a previous sound. As results, the threshold was decreased when the previous sound was presented in the contralateral ear at all previous sound SPLs, and the threshold decrease level became larger significantly as the SPL of the previous sound increased in some experimental subjects. This result shows the threshold decrease phenomenon has a tendency in which the effect is enhanced depending on the previous sound SPL. On the other hand, in the ipsilateral ear, the threshold was increased by presenting the previous sound. And the threshold increase level became smaller significantly as the SPL of the previous sound increased in some subjects.