PROBLEM TO BE SOLVED: To count a particle size distribution (particle number) with respect to a particle diameter with high accuracy in the case that the particle diameter is large and even in the case that a state in an atmospheric air is unknown. SOLUTION: Voltage being reference to be applied to form an electric field is set to a voltage value U, and classification of aerosol particles is executed by electrical mobility in the electric field applied by the voltage value U. When a predetermined condition is not satisfied, what is obtained by further adding the voltage value U to a voltage value (previous value) of the voltage applied when classified at the last time is reset as voltage to be applied to form an electric field. The classification of the aerosol particles is re-executed by reset electrical mobility. The first measurement result is defined as a measurement result M1, a new measurement result Mx is defined in each measurement repeated by re-measurement means. A ratio between the measurement result M1 and the new measurement result Mx is calculated, and it is determined that the condition is satisfied when the calculation result is less than a specified value, and that the condition is not satisfied when the calculation result is larger than the specified value. COPYRIGHT: (C)2013,JPO&INPIT
