For transmitting olfactory information together with audio/visual information in the field of multimedia, it is necessary to control the scent presentation in accordance with the changing images and sounds presented to receivers. However, continuous emission of scents creates problems of lingering scent in air and human olfactory adaptation. To overcome such problems we applied repeated pulse ejections to emit a scent for short periods of time. We remodeled an olfactory display having high emission control ability. This display can control emit for a unit of 667 μsec. It has been found out that the shortest time of pulse ejection which everyone can sense is 33 msec in this preliminary experiment. So we measured olfactory characteristics for 33 msec of pulse ejection. "Response time" and "Duration of scent perception" were measured for pulse ejection. Further, we defined and measured the minimum ejection interval that subject could discriminate the two individually emitted pulses of scent, which we call "Separable detection threshold". It is expected that scent presentation based on these results can match visual and audio information and better enhance the sense of reality.