Disclosed is a configuration to implement a robot replacement in a library apparatus while maintaining an electrically-activated state. In such a configuration, the library apparatus storing a recording medium (cartridge) for writing and reading information with a host computer, comprises a plurality of robot units, which carries the recording medium; and a control unit (library control unit) which stops power feeding to the robot units if an event is generated until processing time of the event or predetermined time elapses and which transmits to a query from the host computer a response representing that the processing of the event is in progress.