In order to investigate an influence of indoor sound environment in office on knowledge creative activity, subjective experiments were conducted in our study. In this experiments, subjective evaluations on “ease of meeting”, “quietness of sound environment” and “listening difficulty of speech” in two different types of group meetings (decision-making meeting and discussion to think of creative ideas) were measured under five types of sound environmental conditions (no-noise LAeq, 5min 38 dB, ambient noise (conversation noise) LAeq, 5min 40 dB, 45 dB, 50 dB, 60 dB) in a meeting room of the university. From the results, in regard to “quietness of sound environment”, we found that subjects start feeling noisy (not quiet) in sound environmental condition of ambient noise 50 dB, and that of 60 dB have an increased “listening difficulty of speech”. In the ambient noise 50 dB, “ease of meeting” was the highest evaluation for discussion to think of creative ideas among these experimental conditions. Furthermore, to investigate psychological factors related to ease of meeting, multiple regression analysis was performed using the data obtained from subjective experiments. These results of multiple regression analysis show that a quiet sound environment is not necessarily desirable in discussion to think of creative ideas. It was found that very quiet sound environment decrease the evaluation of “ease of meeting” in discussion to think of creative ideas. Thus, it was suggested that recommended indoor sound environmental condition to conduct discussion to think of creative ideas was ambient noise 50 dB.
