A stopper mechanism of a slide rail for protecting a slide rail that is attached to a housed unit has an auxiliary slider that moves to a first position so as to become closer to the housed unit in a state where the housed unit is housed in a main body, and which moves to a second position so as to become more distant from the housed unit in a state where the houses state has been pulled out of the main body, and a stop unit configured to stop the pulling-out of the housed unit by stopping the auxiliary slider that has moved to the second position.