This article attempts to introduce the role and functions of museum and to present the mission of a museum in the 21st century. According to definition of ICOM 2004 Seoul. a museum is defined as a non-profit making permanent institution in the service of the society and its development open to the public, which acquires , conserves , researches , exhibits , for purposes of study, education and enjoyment, both tangible and intangible evidence of people and their environment. In general. a museum has functions with 4 parts: acquiring, keeping and documentation, exhibition, and not only research but also education. Acquiring is a way to collect museum materials including objects and specimens. Keeping and documentation are to keep and to document museum materials by specified collection, documentation and information system. It is important function because museum materials are not someone's collection but national properties. So a museum has to need high-technological storage facilities and more studying about that. Above all , exhibition is the most important thing. A museum is the place that people use their spare moments which augments more than past. Therefore , a museum have to renovate their static image and improve in 'approaching museum' as a multi-space of education to public. Research is one of factors to decide a level and quality of museum. Museum users get some information not only observation but also understanding collections through materials which the products of studying. And a museum utilizes vary activities for education as the view of offering public service. A museum is a center for our culturallife. But, unfortunately, our society doesn't have enough cultural-perception and economic power and there isn't systematic supporting. So, a museum has not performed basic functions which refer this article perfect1y, especially the case of private museum. But a museum is progressing now. We should accept this innovation in affirmative point of view for the time to come.