To provide an avian influenza infection preventing means and a preventing method which do not exert harmful effects on the natural environment, are safe for animals and plants including chicken and humans, not complex and effective.

Cages 2 for raising chicken C are installed in a poultry house 1A. A feeding-water supplying part 3 as a feeding part for supplying food and a water supplying part for supplying drinking water is attached anteriorly and inferiorly to each of the cages 2. An ozone generating device 10 is installed outside the poultry house 1A. Piping 20 for applying ozone from the ozone generating device 10 into the poultry house 1A is installed. The piping 20 is composed of a pipe 21 for introducing ozone from the ozone generating device 10 from the outside into the inside of the poultry house 1A and three pipes 22, 23 and 24 for dispersing ozone from the pipe 21 from the ceiling. The pipes 22-24 have numerous pores for blowing out ozone downward.