To realize a small and compact device and stably measure both positive pressure and negative pressure with high accuracy.

The pressure detecting device 1, which is composed of a unit mounting member 3 being mounted at a prescribed mount position Xc of a containing section 2 wherein a medium to be measured L is contained and having a pressurized space 4, and a pressure detecting unit 5 being attachable to and detachable from the unit mounting member 3 and having a pressure detecting surface 6 facing the pressurized space 4 at an end section Fs, includes a seal holding member 7 that is disposed from the unit mounting member 3 to the pressurized space 4, a seal member 8 that is disposed between the seal holding member 7 and the end section Fs, and a fixing member 9 that can fix the pressure detecting unit 5 to the unit mounting member 3 through the seal member 8.