In a master-slave system, operators control the master device based on visual information and sensory feedback. This suggests that the position sensors on the slave side are not always necessary. However, position signals are required to estimate the acting force conveyed to the slave using an observer which realize the force sensorless control. In this paper, we focused on the biological signals of the operator to estimate the slave side’s condition which can be used to estimate the external force. In the early stage of the research, we investigate biological signals just with 1-DOF masterslave system. First, we measured electromyographic (EMG) and gripping force of operators when pushing objects. We verified that predictive signals can be used for estimation of touching the objects. Second, we propose a method, which uses wrist joint torque and Total Contraction Level (TCL) calculated by the EMG when pushing the virtual elastic films, of estimating the acting force conveyed to the slave. We verify that the proposed method can estimate external force under specific conditions with a trained subject.