Robots have entered human life, and closer relationships are being formed between humans and robots. It is desirable that these robots be flexible and lightweight. For this reason, we studied and developed an artificial muscle actuator using straight-fiber-type artificial muscles derived from the McKibben-type muscles, which have excellent contraction rate and force characteristics. Therefore, we developed a 6-DOF artificial muscle manipulator, which has a wider moveable range than that using McKibben-type artificial muscle. However, this manipulator vibrates when receiving a sudden load, because the artificial muscle is flexible. For this problem, we suggest that control of joint stiffness is effective. In this paper, we controlled joint stiffness of the 6-DOF artificial muscle manipulator, and obtained a compliance ellipse of the end-effector. In addition, this manipulator controlled vibration of the end-effector by changing joint stiffness depending on the position of the end-effector.