The averaged evoked potentials by the pips were examined in active and passive attention. In passive attention, the subject's attention was aroused by the external stimulus which was changed unexpectedly as the warning signal to the following discrimination task. Zn active attention, the subject had to direct his attention to the discrimination stimulus. In passive attention, the marked positive component with latency 350 cosec was observed. In active attention, the amplitude between the negative component with latency 80 cosec and the first positive peak with latency 180 cosec was enhanced. These facts were explained by Sokolov's theory of the nervous model.