A bus is placed at the center of a housing. Breakers and cables forming branch circuits branching from the bus are placed at the upper and lower stages in the housing, being displaced in the right-left direction. Spaces formed between the side wall of the housing and the side walls of an upper-stage breaker compartment and an upper-stage cable compartment containing the upper-stage apparatuses are used as paths leading to the housing ceiling for a bus compartment, and a lower-stage breaker compartment and a lower-stage cable compartment containing the lower-stage apparatuses. The bus compartment and all the apparatus compartments each directly lead to a ceiling portion of the housing and have an opening portion. Pressure discharge plates are provided on the opening portions.