Upon receipt of a read command or a write command from an external device, a disk apparatus stores an obtained address as a primary address and a secondary address in an address storing unit, increments a counter value of the secondary address, and selects the secondary address of which the counter value indicates the largest number. Upon receipt of the read command for the primary address, the disk apparatus reads data specified by the primary address from a disk and stores it in a buffer memory in advance. Upon receipt of the read command, the disk apparatus sends the data from the buffer to the external device.