In this paper, we discuss complementarity and substitutability of ICT (Information & Communication Technology) on face-to-face meetings in office concerning process. Findings from the analysis demonstrate that existing ICT (E-mail) is used for such as documents pre-sending complementary to meeting process, forming perception which new ICT (EMS) would produce advantage is greatly important to substitute face-to-face meeting, and it is effective for formation of the perception to make workers utilize electronic media more frequently in the meeting process. This improvement of those kinds of perception will lead office workers to use media low in richness at communication in high equivocality.