A condensation particle counter measures the number of ultra-fine particles by growing the ultra-fine particles through a condensing process. The counter includes a capillary in which vapor of operating liquid is condensed and the ultra-fine particles grow. An insulating material surrounds the capillary to shut out heat flow between the capillary and the environment. The condensation particle counter can use various operating liquids including alcohol and water, and can be also applied to semiconductor clean rooms.