1. A command execution device, comprising: a behavior type decision unit which decides a behavior type indicating the content of data input/output operation, according to the content of data processing executed by an entered command; a command storage unit which refers to setting information set in advance for each of behavior types, and stores the command in a command queue created for each priority level, based on the priority level included in the setting information; and a command execution unit which fetches, out of the commands stored in the command queue, a command stored in a section of the command queue having the highest priority level from the command queue, and executes the command.