To provide a storage system that can control both the number of commands activated per unit time and the response time of each command activated in accordance with the priority level of command. The storage system comprises a queue corresponding to each priority of command and an activation order control part. A command that the storage system receives from a host computer is accumulated in the queue corresponding to the priority specified from the command. The activation order control part decides, for each queue, the number of activation object commands that are the commands to be activated among a plurality of commands accumulated in the queue, based on the priority corresponding to the queue. And the activation order control part decides the activation order of the activation object commands, based on the activation object command number decided for each queue, so that the average value of logical response time of the activation object command may be shorter at the higher priority. The activation object command is activated in accordance with the decided activation order.