Pressure measuring instrument and substrate processing apparatus provided with the pressure measuring instrument

A pressure measuring instrument that, using a diaphragm disposed between a reference pressure chamber and a measurement pressure chamber, detects a deformation of the diaphragm and consequently measures a pressure of the measurement pressure chamber, the pressure measuring instrument comprising:

• a detecting unit including the reference pressure chamber therein and formed in a cylindrical shape, the diaphragm being disposed inside the detecting unit;
• a communicating unit for providing communication between the diaphragm and the measurement pressure chamber, and formed in a circular tube shape having an inner diameter smaller than an inner diameter of the detecting unit;
• and
• an annular flow-path forming unit disposed between the detecting unit and the communicating unit, and configured to form a substantially annular path,
• wherein the communicating unit configured to introduce a gas of the measurement pressure chamber into the substantially annular path, the annular flow-path forming unit configured to allow the gas introduced from the communicating unit to pass through the substantially annular path and to supply the passing gas to a side surface of the diaphragm, and the substantially annular path is formed at a location opposite to a location at which a differential value of a displacement of the diaphragm reaches a peak.