are opened and electromagnetic valve 5e is closed during the ozone desorption period but water is not then sucked from electromagnetic valve 5e during a period other than the ozone desorption period opposite valve conditions exist water ejector 10 undergoes higher hydraulic pressure and even leakage occurs in electromagnetic valve 5c2 leakage water being discharged out of the system because of electromagnetic valve 5e being opened thereby preventing water flowing into the adsorption desorption tower 2 in the conventional apparatus a non leaking type electromagnetic valve useful in providing complete cutting off of gas or liquid has been used for electromagnetic valve 5c2 such non leaking valve is rather expensive and has a relatively short life span in accordance with the structure of embodiment of the present invention allowance of a little leakage occurs and a specially constructed electromagnetic valve is not required and accordingly the manufacturing cost can be reduced the same effect can be obtained by utilizing a check valve instead of electromagnetic valve 5e fig8 is a schematic view of another embodiment using a check valve 21 check valve 21 allows the flow of fluid from the intermediate portion of electromagnetic valves 5c1 5c2 toward the exterior of the system the open end that is water leaking from electromagnetic valve 5c2 is discharged and prevents the flow of the fluid in the opposite direction that is environmental air is.