This study proposes an estimation method of the masticatory forces using an objective function composed of three criteria: efficiency of muscular activities, moment balance between muscular and biting forces, and reaction forces at condyles. Our previous study applied the method to a patient whose jaw had a severe deformity, and showed validity of the method. This paper applies the method to a patient with a symmetrical jaw. The numerical result shows an unrealistic masticatory condition, such as there are non-working muscles. The plausible solution of this problem is discussed.