A stapler is provided with a driver support part which supports an actuating mechanism of a driver; a clincher support part which is arranged apart from the driver support part in an up/down direction and to which a clincher is fixed; a positioning member provided in a vicinity of one of the clincher support part and the driver support part; a first positioning element provided on the positioning member; and a second positioning element provided on the one of the clincher support part and the driver support part. The driver support part and the clincher support part are simultaneously movable in a right/left direction by substantially the same amount. In cooperation with a clamping operation, the first positioning element and the second positioning element engage with each other.