CRS (Curved Rail Safety Device) is one of the safety devices of the escalator. With the feature with a wide range of detection, zone type CRS is often adopted. In the zone type CRS, an operation track is generally set up along the traveling direction of the step at the upper and lower curved section of escalator. And the rise of the step due to catching shoes between step is detected as displacement of the operation track. In this type CRS, it is preferable that the operation force is constant in the whole area within the range of detection. In this paper, the conditional equation that the operation force is constant is derived. CRS with nearly constant operation force is designed, and the validity of the design is confirmed by the experiment