Abstract
The number of actors, orchestra and staffs of Muscial and the spatial composition of backstage of ten musical theaters in Korea are investigated. Ancillary spaces of backstage are categorized into four sections on the aspects of user and uses for the space. Average area and the ratio of each categorized spaces are researched. The largest area of backstage is the space, which is for preparing and for stage set. The unit area of dressing room per a person is changed from $2.4m^2$ to $6.4m^2$, and the unit area of dressing room is increased propotional to size of theater. Cross-sectional composition of backstage spaces are investigated also.