A sensor substrate 1 having on its lower surface a surface acoustic wave element 2 for detecting pressure is mounted on a supporting substrate 6 through a sealing member 4 surrounding a sensor section 2. A sealing space S is formed by the sensor substrate 1, the supporting substrate 6, and the sealing member 4, and the surface acoustic wave element 2 for detecting pressure is sealed hermetically in the sealing space S. Reliability can be enhanced by protecting the surface acoustic wave element 2 from the external environment.