The museum houses the collections of the Mitsui family and Mitsui Group, one of the most powerful zaibatsu in Japan. The museum was formerly located in Nakano Ward, but moved to Nihombashi—an area to which the Mitsui Group more generally has deep connections—in 2005. The collection consists of over 4,000 exhibits including tea ceremony utensils, Noh theatre costumes and masks, and 130,000 postage stamps. Among the exhibits are six items designated as National Treasures, and many more that have been given the status of Important Cultural Property. Temporary exhibitions are also hosted at the museum.
