It is commonplace these days to hear that some electrical precipitators are operated with unsatisfactory states. The minor enterprisers say that it is difficult to estabrish the precipitator easily for its high initial cost. The plan of an electric precipitator equipment is to be discussed safficientry. As result on the experiments the author suggests author's point of view for the relation between collecting phenomena in various industry equipment and the economical cost of an electric precipitator. 1) The collection efficiency η_w relating mass collected and η_s relating covering power of the exhaust smoke of an electric precipitator should be handled with different meaning as for fume or mist nature and cleaning condition. 2) At an electric precipitator design the higher all day efficiency can be given with little increase in equipment cost. 3) The gas cleaning cost (Y/Q) may be a little higher for minor enterprises, but minor enterprisers must study the utilization of collected substances for economical plant operation. Where, Y : Economical cost for E. P. installation and running Q : Gross gas volume to be handled