This study aims to develop a palpation sensor that can obtain both surface and inside information of objects. The palpation sensor using bimorph cell is proposed. The sensor is combined with an encoder in order to obtain traveling distance and velocity as position information of the sensor. In this paper, signal processing for measurement of surface smoothness, one of important surface information, is investigated. Using the sensor, fine polishing papers are measured. Frequency analysis of sensor output applied the velocity compensation using encoder signal is carried out. As a result, linear relationship between its mean power frequency and particle size of polishing paper is obtained. It is found that smoothness can be measured using the relationship without control of scanning velocity.