To provide a diaphragm seal type pressure difference measuring device capable of preventing a flush ring from being dropped from a diaphragm seal block during piping workpiece.

In the diaphragm seal type pressure difference measuring device including a diaphragm seal unit having a pressure receiving block and connected to a differential pressure measuring device body via a connecting pipe and the flush ring having one surface in contact with one surface of the pressure receiving block, the diaphragm seal type pressure difference measuring device includes: a pair of plate-like holders having one-end sides fixed to the flush ring and the other-end sides holding the peripheral surface of the pressure receiving block incorporation with each other; a locking nail provided to the other end of the plate-like holder perpendicularly; and a locking groove facing the locking nail and provided at the pressure receiving block so as to lock the locking nail.