In this paper we propose a new robust force and position control method for property-unknown objects grasping. The proposed control method is capable of selecting the force control or position control, and smooth and quick switching according to the amount of the external force. The proposed method was applied to adaptive grasping by three-fingered hand which has 12 DOF, and the experimental results revealed that the smooth collision process and the stable grasping is realized even if the precise surface position, the mass and the stiffness are unknown. In addition a new algorithm determines the grasp force according to the "slip" measured with the tactile sensor and the viscoelastic media on the fingertip. This algorithm works at starting and stationary state, so the friction and mass unknown object grasping is realized by the effectual force.