The force of a sinusoidal wave is applied to a sample to measure the phase difference on how much the deformation of the sample is lagged behind the force that is applied. For this purpose, the device comprises the sample, a force generator, a timing circuit, a zero-cross detector, a t1 measuring instrument, a t2 measuring instrument, and a phase difference calculating device. The phase difference calculating device calculates a correction using a time t1 (phase difference containing error) from a zero-cross point of a sinusoidal wave of the force measured by the t1 measuring instrument to a zero-cross point of the deformation of the sample, and a time t2 from a zero-cross point of the deformation of the sample measured by the t2 measuring instrument to a next zero-cross point. The phase difference is correctly found even when the zero-cross point is shifted as a result of superposition of DC components on the deformation of the sample due to deformation by thermal expansion and creep phenomenon.