An input/output apparatus according to the present invention has an indication unit and an execution unit. The indication unit indicates that each of a plurality of data blocks between a main memory and a buffer memory is to be transferred. The execution unit transfers one data block relating to a transfer indication sent from the indication unit. After the completion of the transfer, in order to send completion information relating to the one data block to the indication unit, the execution unit determines whether transfers of all of the plurality of data blocks are completed or not based on management information for managing progresses of the transfers of the plurality of data blocks. Once determining that all of the transfers are completed, the execution unit sends, to the indication unit, total completion information showing that all of the transfers are completed.