PURPOSE: To improve accuracy by sampling momentarily load values by a load detecting part based on a zero method when a thin cylinder is separated from the surface of liquid to be measured in a water tank, storing its maximum value, and obtaining surface tension by conversion.

CONSTITUTION: The liquid L to be measured is charged in the water tank 7 and a handle 61 is operated so that the liquid surface contacts the lower end surface of a detector 9 hanged from a measurement data part 1a through a hook 8 in parallel. When the liquid surface is brought into contact with the thin cylinder 91, drawing-down force based upon surface tension operates upon the cylinder 91, but the cylinder 91 is returned to a balance position instantaneously through the operation of a load detecting part 1 of an electromagnetic force balance type scale using the zero method. A zero adjustment of a detected load is made in this state with an operation key 3 then the water tank 7 is jogged with the handle 61 so that the cylinder 91 leaves the liquid surface, and the value W at the moment when the cylinder 91 leaves the liquid surface while force stopping the leaving of the cylinder by surface tension is maximum is calculated. Further, the surface tension is calculated by a CPU21 from T=W×g/2π(R1+R2), where (g) is gravitational acceleration.