Recently, Minimally Invasive Surgery (MIS) that has some advantages has come to the front. The research on surgical robot for operational support has been actively done. To use such robots in MIS, it is needed to estimate the environmental impedance as the numerical data and to preserve it from the viewpoint of knowing the standard reference value of the safety field of internal organs and from that of the support of education for the operation. In this paper, a novel method for the estimation of environmental stiffness in a real environment by bilateral control is proposed. In this method, one degrees of freedom linear motor is used. And it enables environmental stiffness to be estimated with an environmental reaction force by the reaction force observer based on the disturbance observer. It is able to estimate environmental stiffness without depending on slave's initial position. Moreover, the stiffness is enabled to be estimated dynamically by using past information. To verify the viability of the proposed method, experimental results are shown.