An electrorheology (ER) effect of a ferroelectric liquid crystal (FLC) is described on the basis in numerical analysis and experiment, Propagation characteristics of a Shear-horizontal (SH) wave in a liquid crystal layer between a piezoelectric ceramic thin plate and a glass thin plate is numerically analyzed. The phase velocity of the SH wave depends predominantly on the viscosity of the FLC. The ER effect is measured using a SH wave device under the construction of delay line oscillator. The observed DC electric field dependence of oscillation frequency under the use of a helical structure of FLC is related to the observed microscopic result. This method has the advantage of simplicity and a small amount of liquid sample for evaluating the ER effect of the FLC.