To produce the subject ether in an extremely high yield by using completely halogenated ethylene.

(B) C3F6 and/or C2F4 is subjected to photooxidation at -20 to -100°C by using (C) an oxygen gas in the presence of (A) a perhalogenated ethylene containing at least one halogen atom different from fluorine while irradiating the liquid reaction mixture with ultraviolet rays and then successively the-peroxide group is removed by heat treatment at 180-220°C or photochemical treatment by ultraviolet light irradiation to give an ether of formula II [X is F or CF3; R and R' are each F, Cl or the like; Y is a group of formula III; T is A log CF2- or the like; A log is Cl, Br or the like; n is 1-5; m/n is 0.01-0.5] comprising a sequence in which a perfluorooxyalkylene units of formula I, etc., are randomly distributed, containing an acid terminal group and the other terminal group which is a perfluoroalkyl containing a halogen atom except fluorine.