To improve a responsivity and a temperature characteristic.

A diaphragm 15 in touch with a liquid and a diaphragm 35 for preventing and overloed are arranged symmetrically at both side faces of a detector body 17 of a pressure detector 3. Diaphragm chambers 16 and 37 formed by the diaphragms 15 and 35 are communicated with each other via communication path 38. The communication path 38 is connected to a capillary tube 5 via a sealing liquid path 18. A compliance of the diaphragm 35 is set to be smaller than that of the diaphragm 15. When the diaphragm 15 shifts, a sealing liquid 20 is the diaphragm chamber 16 moves through the communication path 38 to the diaphragm chamber 37, thereby shifting the diaphragm 35. Only a pressure at this time is transmitted to an oscillator main body 2 via the capillary tube 5.