To provide a differential pressure measuring apparatus having a protection diaphragm with specified tension in the radial direction and sufficient corrosion resistance, and to provide a method for manufacturing the differential pressure measuring apparatus.

The diameter of the protection diaphragm 3a at a protection 2a is set to be the next smaller size than the external diameter of a pair of bodies 4Aa and 4Ba arranged at both the sides of the protection diaphragm 3a. A counter sinking section having a diameter slightly larger than that of the protection diaphragm 3a is formed on a surface at the side of the protection diaphragm 3a of the body 4Aa. The protection diaphragm 3a is clearance-fitted into the counter sinking section. The outer-periphery internal surface of the counter sinking section is butt-welded to the outer-periphery surface of the protection diaphragm 3a (the formation of a welding section 9). Then, the bodies 4Aa and 4Ba are welded at the outer periphery section (formation of a welding section 10) and the protection diaphragm 3a is set to be in an included state.