[en] The large-volume multiwire pulse ionization chamber for the ions collection was examined as the α-particles detector from the radon decays in the air inside the chamber. The possibility was also studied for obtaining the spectrometric information from the slow ion pulses. The energy resolution of 3.9% for the 5.49 MeV α-particles was obtained in the preliminary measurements. It was shown, that the detector of such type might be applied for direct measurements of the radon activity in the flow-through air at the level lower than 1 Bq/m³. The radon concentration at the level of 10 Bq/m³ may be measured with the accuracy better then 10% for the 10³ s counting time. The detector will be used for the ²²²Rn continuous accurate monitoring in the air of the underground laboratories