To obtain a correct quantity of sample by providing a counter between a suction nozzle and a filter and then counting the sucked particles.

Particles are stripped off from the surface of a wafer 2 by blowing the air from a blow-out nozzle 5 and then sucked through a suction nozzle 1. The sucked particles pass through a particle counter 12 when they are caught on a filter 4 and the number of sucked particles is counted. Catching of particle is stopped when a predetermined count is reached in the particle counter 12. Since the particles are caught based on the count of particle counter 12, correct quantity of sample can be caught on the filter 4.