PROBLEM TO BE SOLVED: To improve the detection accuracy of boarding allowance in which a limb walking animal allows boarding behavior. SOLUTION: The sensor 10 according to the present invention is a sensor attached to the back of a four-legged walking animal for detecting the permission of the two-legged walking animal to allow a riding action by another four-legged walking animal. The electrode layers 123A and 123B are provided on both surfaces of the ion conductive polymer layer 122, and the polymer element 121 has a polymer element 121 that deforms in response to the application of a load and outputs a signal according to the deformation. It is provided in a non-planar shape when no load is applied. [Selection diagram] Figure 1【課題】四肢歩行動物が乗駕行動を許容する乗駕許容の検知精度の向上を図る。【解決手段】本発明に係るセンサ１０は、四肢歩行動物の背に取り付けられ、該四肢歩行動物が他の四肢歩行動物による乗駕行動を許容する乗駕許容を検知するためのセンサであって、イオン導電性高分子層１２２の両面に電極層１２３Ａ，１２３Ｂが設けられ、荷重の印加に応じて変形し、該変形に応じた信号を出力するポリマー素子１２１を有し、ポリマー素子１２１は、荷重が印加されていない状態において非平面状に設けられている。【選択図】図１
