This paper presents the design and stiffness modeling of a new 3 DOF soft finger mechanism using a spring as a backbone. The mechanism consists of a spring and 3 cylinders, which behave like joints. To control each joint, wires of different length are penetrated into the cylinders which have small holes in their cross-sectional areas, and each joint can be controlled by pulling each wire. Also, the stiffness modeling is conducted to measure the softness of the finger mechanism as well as to estimate the actuator size. First, the forward kinematics is solved by using the geometry of mechanism, and length of wires and Jacobian are obtained. In order to evaluate the efficiency of the proposed mechanism, the position control, the flexibility and safety, and the stiffness model are verified through experimental work.