This Paper presents a novel evaluation method by measuring user's brain wave. In the experiment, we measured the user's brain wave when the user controlled the virtual arm with each easy and difficult position to control. As a result, the spectrum of the brain wave increased at easy position more than difficult position (t=1.681, df=7, p<0.1). We conclude that the brain wave changed as the user perceives that the virtual arm belongs to the user's body.