Paramecium caudatum, a kind of ciliates, exhibits very strong galvanotaxis; when a DC electric field is applied, cells are made to swim toward the cathode. In this article, we propose a novel physical scheme for Paramecium galvanotaxis to provide a quantitative explanation, using a bottom-up approach based on systems theory. We analytically derived the torque produced with respect to the cell angle and constructed equations of translational and rotational motion. Using the proposed model, we performed numerical simulations. We also performed a preliminary evaluation of the proposed model by using real data. Experimental data were obtained by using a real-time galvanotaxis observation system developed in our laboratory. We found that the simulated data was approximately in agreement with the experimental results. [Arranged from (Ogawa et al. 2005) and (Ogawa et al. 2006)].