There are three former studies dealing with tone effects on successive comparison of brightness (SCB), considered as a kind of intersensory interaction. These studies found contradictory results of tone effects (facilitation, no effect, and inhibition). The present study examines the assumption that tone frequency difference may cause the above contradiction. As sensory interaction among senses is small and fragile, the most effective conditions of tone stimuli (timing and intensity) on SCB were searched for a start, and then the effects of tone frequency on SCB were investigated by using these effective conditions. The timing of auditory stimuli (1000 Hz, 80 dB pure tone) was varied in Experiment 1 and the tones were presented "just before", "synchronically with", and "just after" the visual stimulus. In Experiment 2, three intensities (40, 60, and 80 dB) of auditory stimuli were scrutinized. Then, using these conditions (80 dB pure tone presented synchronically with the visual stimulus), the frequency effects were examined in Experiment 3. The assumption was partly confirmed; high frequency tones facilitate brightness and middle frequency tones show no effects but no inhibition was found, and another cause of the contradiction, individual difference, was suggested.