The disk array system includes: controller modules, power source modules, and battery modules of a basic chassis; enclosure modules and power source modules of an expanded chassis; and operation levers which are commonly used for operations of insertion/removal and fixation of the modules. The operation lever includes a rotary shaft portion serving as a fulcrum point, a lever main body and a latch portion located on one side of the lever, and a hook portion located on the other side thereof. When a module is inserted and fixed, a user rotates the lever main body. By this means, the latch portion and the hook portion are fixed to a receiving portion and the module is connected and fixed to the backboard with a connector.