This paper proposes a new four degrees-of-freedom (dof) humanoid foot device that can allow humanoid robot to walk naturally like normal human. The device can generate rotations at two toe joints and two rotations at ankle. The new mechanism consists of front-left, front-right, and rear platforms, and four limbs. Base of three platforms is located at a humanoid shin. One limb with 6-dof serial joints (S-P-U) is attached to front-left and front-right platforms, respectively, while rear limb (Pe-Re-R) and four-bar limb (S-S) are attached to rear platform. The rear limb is driven by the 2-dof driving mechanism (Pe-Re) with two base-fixed prismatic actuators. The four-bar limb will allow the rear platform to generate pitch motions. A new 4-dof mechanism with three platforms can generate pitch and roll motions at each platform. Kinematic analyses of the suggested mechanism were performed, including inverse and forward kinematics, and velocity analysis. Based on this mechanism, the foot device was developed for natural walking of humanoid robot.