A stapler comprising: a main body; a magazine having a pair of sidewalls and a tip end wall and configured to be movable between a first position at which the magazine is inserted in the main body and a second position at which the magazine protrudes from the main body, a staple being capable of being taken in and out from an opening formed above the pair of sidewalls and the tip end wall when the magazine is located at the second position; a driver located above the magazine and configured to be movable toward the staple in the magazine when the magazine is located at the first position, the driver being configured to move toward the staple, thereby striking the staple into a sheet bundle set below the magazine; a clincher arranged below the magazine and positioned to face the driver when the magazine is located at the first position, and configured to receive and bend leg portions of the staple penetrating the sheet bundle by a striking operation of the driver; a cover attached to the main body so as to be displaceable between a third position at which at least a part of the cover is positioned on a moving path of the magazine and a fourth position at which the entire cover deviates from the moving path; a lock part configured to lock the magazine at the first position; and a release button configured to release the locked state, wherein when the cover is located at the third position and the magazine is located at the second position, the cover covers the pair of sidewalls, the tip end wall and the opening of the magazine in a state of protruding from the main body, and characterized in that the release button is located inside of the cover when the cover is located at the third position such that only when the cover is located at the fourth position at which it is opened, a user's pressing operation on the release button can be received. a main body; a magazine having a pair of sidewalls and a tip end wall and configured to be movable between a first position at which the magazine is inserted in the main body and a second position at which the magazine protrudes from the main body, a staple being capable of being taken in and out from an opening formed above the pair of sidewalls and the tip end wall when the magazine is located at the second position; a driver located above the magazine and configured to be movable toward the staple in the magazine when the magazine is located at the first position, the driver being configured to move toward the staple, thereby striking the staple into a sheet bundle set below the magazine; a clincher arranged below the magazine and positioned to face the driver when the magazine is located at the first position, and configured to receive and bend leg portions of the staple penetrating the sheet bundle by a striking operation of the driver; a cover attached to the main body so as to be displaceable between a third position at which at least a part of the cover is positioned on a moving path of the magazine and a fourth position at which the entire cover deviates from the moving path; a lock part configured to lock the magazine at the first position; and a release button configured to release the locked state, wherein when the cover is located at the third position and the magazine is located at the second position, the cover covers the pair of sidewalls, the tip end wall and the opening of the magazine in a state of protruding from the main body, and characterized in that the release button is located inside of the cover when the cover is located at the third position such that only when the cover is located at the fourth position at which it is opened, a user's pressing operation on the release button can be received.