An information processing device that detects the position of a subject shot by a camera in a three-dimensional space is provided. The information processing device includes a depth image acquiring section that acquires a depth image in which the distance of a subject in the depth direction from the camera is represented as a pixel value on an image plane, a spatial structure identifying section that identifies the position of a plane forming a predetermined angle with a gravity vector among subject surfaces by detecting a coordinate point collection representing the plane on the basis of the distribution of coordinate points obtained by inverse projection of pixels of the depth image to the three-dimensional space based on the direction of the gravity vector, and a target object extracting section that generates and outputs position information of a predetermined target object on the basis of the position of the plane.