Feature integration theory and parallel process model have been described how and when multiple features of objects are processed and integrated. These studies dealt with only integration of physical features such as color or orientation of bars. We can instantaneously identify not only physical information but also cognitive information. Here, we studied integration of a physical feature and a cognitive feature using event-related potentials. In this study, colored numerals were presented serially on a monitor. Participants had to determine their response to the stimulus according to either the color (i.e., red or black; Color condition), the numerical attribution (i.e., odd or even; Number condition) or the combination of these features (Conjunction condition). N100 and N200 were chosen as an index reflecting selective attention. P300 was also employed to study stimulus evaluation time and cognitive effort. Results showed that the amplitude of N100 and N200 under the Conjunction condition was not different from that in the Number condition but larger than that in the Color condition. In addition, response time and P300 latency in the Conjunction condition were not different from those in the Color condition but shorter than those in the Number condition. These findings indicate that physical feature is processed automatically even in the condition where this feature is not relevant for the task. In other words, physical feature and cognitive feature are processed in parallel.