In this study, practical friction coefficient between a wafer and a carrier during double-sided lapping was investigated. The friction coefficient was identified from the rotational speed of the wafer, which was measured in the single-sided lapping experiment on a double-sided lapping machine, based on the equilibrium of the force and moment applied to the wafer. The identification was conducted under several conditions and it is confirmed that the friction coefficient in the process is not small enough. Hence, it is concluded that the friction between the wafer and the carrier is essential to consider the behavior of the wafer.