PURPOSE: To avoid exerting undue stress on a gas-permeable diaphragm of a gas-sensitive electrode by inserting and reinforcing the outside edge of said diaphragm into and by two annular supports, and attaching the reinforcing part to an electrolytic cell of the gas-sensitive electrode by means of a screw, etc.

CONSTITUTION: A solid-state type glass electrode 1 as a gas-sensitive electrode formed by attaching a gas-sensitive film 3 to the tip of a supporting cylindrical column 2 and a reference electrode 4 such as a silver-silver chloride electrode are inserted and supported in an electrolytic cell 5. The bottom end of the cell 5 is opened to enclose the electrode 1 and a gas-permeable diaphragm 6 consisting of a fluororesin is attached to the open end of the electrode 5. The attaching of the diaphragm 6 is accomplished by inserting and reinforcing first the outside edge of the diaphragm 6 into and by two annular supports 7a, 7b then bringing the central part of the diaphragm 6 into tight contact with the film 3 at the tip of the electrode 1 and fixing the reinforcing outside edge to the open end of the cell 5 by means of a screw 8.