To obtain a differential-pressure measuring apparatus which is assembled easily and whose costs can be lowered by a method wherein the step part of a pressure-receiving part is formed to be a ring shape between the inside resistance-welded part and the outside resistance-welded part of a liquid isolation diaphragm, a deep-drawn part is formed so as to correspond to the step part and a cover flange which presses the peripheral side from a deep-drawn part on the other face is installed.

By inside and outside resistance-welded parts 31, 32, 35, 36, peripheral edges of liquid isolation diaphragms 33, 34 are seam-welded to a pressure-receiving part 1B to be a ring shape. Step parts 37, 38 are formed at the pressure-receiving part 1B to be a ring shape between the inside and outside resistance-welded parts 35, 36, 31, 32. Cover flanges 2, 3 press, the peripheral edge side from a deep-drawn part 3a by deep-drawn parts 39, 41 and the diaphragms 31, 34. In this manner, a pressure force is absorbed by the cover flanges 2, 3 in the deep-drawn parts 39, 41. It is possible to obtain a differential-pressure measuring apparatus in which the initial tension of the diaphragms 33, 34 is not excerted and in which there is no fear that the characteristic of the apparatus becomes irregular. The diaphragms 33, 34 can be welded directly to the pressure-receiving part 1B by a resistance welding operation, an isolating liquid and an intermaterial ring are not required, and the costs of the measuring apparatus can be lowered.