To provide a quiet radioactive dust monitor with excellent portability by reducing the size and weight, stably continuously operable over a long period by eliminating a movable part, and extensible in settable range by generating no exhaust gas.

This radioactive dust monitor comprises a duct collecting electrode (light shielding film 20) used also as a radiation detecting surface, an ionization line 22 laid in the air with a space to the dust collecting electrode, and a radiation detection part 24. The radiation detection part comprises a scintillator layer 30 arranged adjacently to the dust collecting electrode, and a photoelectric conversion part (photoelectron multiplier tube 36) for converting the emission of the scintillator to an electric signal. A negative high voltage is applied to the ionization line, a positive high voltage is applied to the dust collecting electrode to generate a corona discharge, the dust in the air is captured by the dust collecting electrode, and the emission of the scintillator by the radiation from accumulated radioactive dust is detected by the photoelectric conversion part.