Abstract: The invention relates to a chemical breath testing device including a transparent testing tube which cooperates with an outlet piece incorporating a valve and fitted to an inflatable bag. The testing tube is provided with a member for pushing the valve which is formed by the bottom of a cap. The outer sidewall of the cap is resiliently deformable and serves to form an interlocking connection between the testing tube and the outlet piece. The cap is mounted in a mobile manner at the end of the testing tube and carries a cutting blade for cutting a seal closing off the outlet of the testing tube, of which the rim forms a counter-blade.