Computed Tomography (CT)-guided intervention requires an expertized skill to physicians and a numerous of robot-assisted needle insertion system has been developed. As a challenging issue developing the CT-guided needle insertion robot system, the inside of a CT gantry is a special environment where there is no room for movement and no metal can be inserted because of causing an artifact on the acquired image. The gantry entry portion of the robot therefore requires miniaturization and non-metallization. The most difficult part of the non-metallization of a robot is the motor element. While many of the robot's structural materials can be made non-metallic thanks to advances in plastic materials, the actuator cannot be made non-metallic. In this report, we introduce a unique mechanism that enables the needle manipulation with a miniaturized configuration inside the CT gantry. The mechanism satisfies the requirements of power transmission between axes whose relative positions are indeterminate, miniaturization to prevent interference with robot motion, and non-metallization. This mechanism combines a single-node link and gears to transmit rotational power while passively responding to changes in the positional relationship between axes. The hinge fixation of the basic single-node link is aligned with the axis of rotation of the first gear, and the subsequent gears can be freely arranged to mesh with each other. The minimum configuration is 3 gears, one at the hinge, and two at each end. Theoretically, the number of gears can be increased, but it is desirable to use as few gears as possible because transmission accuracy will decrease due to backlash and other factors.  We applied this mechanism to our robot with a 25G needle and inserted the needle into a target from various angles. The accuracy was 2.5 mm and satisfied our requirements.