PURPOSE: To provide an ozone reaction apparatus ground installation space of machines of which is made to be small by making the occupying space of the whole apparatus including a reaction tower and a pump small.

CONSTITUTION: An ozone reaction apparatus consists of an external tower 11 and an inner tower 12 communicated each other in the bottom sides and is composed of a reaction tower 13 having a discharging outlet 14 in the external tower 11, an underwater pump 17 which is set in the center part of the bottom face of the reaction tower 13 while its water supplying part 15 is set to face to the region tower 13 outside and its water discharging part 16 is set to face to the reaction tower 13 inside, a gas jetting pipe 18 which is set in the inner tower 12 in the upper side of the underwater pump 17, a pressure adjusting part 19 to adjust the pressure of a gas accumulated in the upper part of the reaction tower 13, and an ozone leading pipe 20 to inject ozone into the gas jetting pipe 18 from the reaction tower 13 outside.