Device (12) for counting shots fired by an automatic firearm (11), having a cartridge chamber containing a cartridge that can be expelled through an expulsion window and a first emission means that emits a continuous electromagnetic signal in such a manner that it is interrupted by a casing expelled from the cartridge chamber which corresponds to the used cartridge. The shot-counting device (12) of the invention is capable of monitoring the number of casings expelled from a cartridge chamber of the firearm (11) via an expulsion window and showing, on a display screen, the corresponding number of shots left available in a magazine (13) fitted to the firearm (11).