A portable breath analyzing device to measure the rate of partial gas that is exhaled in the breath fluid. The device includes a rechargeable power supply unit, a device to emit pulsated infrared radiation, an infrared receiver, and a measuring vessel. The emission device includes a heating element; the measuring vessel includes a metallic tube whose interior surface is polished and coated with a deposit that reflects at least the infrared radiation of wavelengths that are between (9 μm, 10 μm) and at each end of the tube, a nozzle comprising a cone-shaped section meant to be placed in the tube axis. The infrared emission device is placed on the longitudinal axis of the tube, at the level of one of the nozzles, and the receiver is placed on the longitudinal axis, at the level of the other nozzle.