An jointed tail of a pet robot can be configured simply and driven to curve freely and autonomously by fitting an jointed cylindrical member 25 around outer circumferences of two wire portions 24a and 24b composed of a wire 24 which is folded nearly into a shape of a hair pin, rotatingly driving two driven ends 24d and 24e on a side opposite to a tip 24c of the two wire portions 24a and 24b connected to each other around an X axis and a Y axis with a differential gear mechanism 38, and moving and controlling two driven ends 26d and 26e reversibly in an axial direction at a swing limit position around the X axis, thereby autonomously curving a tip of the wire 24.