To provide an intraocular pressure sensor to realize a higher accuracy sensor system, a simpler structure and a smaller system which is a contact pressure sensor to be used as a tonometer used for an early diagnosis of glaucoma.

The pressure sensor, employing a structure in which the main oscillation of a piezoelectric single crystal serves as a bending oscillation, is built so as to make an oscillation figure conversion section length (L) range from 75% to 92% of a maximum output value. By using the change of resonance frequency or resonance resistance (output voltage) in accordance with the height of the aqueous humor pressure at the time when the leakage energy of a lateral oscillation is emitted into aqueous humor through a cornea, the pressure sensor senses the intraocular pressure.

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