A time-interval based monitor tool is provided for monitoring performance of a running application. The held portion includes an openclose member for openingclosing the toner outlet in synchronization with an attachmentdetachment operation of the held portion tofrom the toner-container holder. This enables the plungers to be attracted independently from each other and results in a decrease in power consumption of the magnetic coils when the plurality of plungers are attracted simultaneously. The bed is completely covered by an insulated arched roof.