Photography is closely tied with people's emotion. Therefore, the concept of emotion driven camera is a natural consequence of future photography. As for EEG emotion detection in research laboratories, there have been many works but it is considered difficult to apply such methodologies in generic environments. For measuring ERP (event related potential), some kinds of cues are typically used for knowing the exact time in which a stimulus given, but it is difficult to know such cues in real world. Therefore, we propose a cue detection mechanism based on the architecture of digital single lens reflex camera. It enables to reproduce an environment similar to research laboratories and is still a natural configuration for ordinary digital cameras.