To simply measure the physical properties of a fluid, especially, the viscosity, surface tension and contact angle thereof with high reliability by utilizing Rayleigh type surface elastic wave (SAW).

The input signal generated by an oscillator 20 is applied to two IDTs to excite the liquid droplet dripped on a circular gold film. The transmitted image of the liquid droplet generated by irradiating the excited liquid droplet with semiconductor laser 21 horizontally is magnified by a lens 22 and the height fluctuations of the apex of the liquid droplet are detected by a semiconductor position detector: PSD 23. The signal detected by this PSD 23 is taken in a computer 24 through a general-purpose interface bus: GP.IB interface. The taken-in signal is analyzed in vibration by the computer 24 and free vibration frequency f0 and an attenuation rate α are calculated. By this constitution, the viscosity, surface tension and contact angle of a liquid are measured.