Improving response time performance by executing exclusive extent processing of a plurality of I/O requests is proposed. A storage apparatus, which includes a plurality of microprocessors, a first memory which stores counter values indicating the order of the I/Os to and from the storage areas, and a second memory which stores control information of the I/O requests for each of the I/O requests, is configured such that the microprocessors store, if there is one I/O request from the host apparatus, an I/O request range of the one I/O request in an area for storing control information of the one I/O request of the second memory, the microprocessors acquire the counter value from the first memory and store the counter value in the area for storing control information of the one I/O request of the second memory, and the microprocessors compare, if the counter value of the one I/O request is greater than the counter value of another I/O request, the I/O request range of the one I/O request stored in the second memory with the I/O request range of the other I/O request.