An information processing device extracts an image of a marker from a photographed image, and obtains a position of a representative point of the marker in a three-dimensional space. Meanwhile, a position and an attitude corresponding to a time of photographing the image are estimated on the basis of an output value of a sensor included in a target object. A weight given to positional information of each marker is determined by using a target object model on the basis of the estimation, and positional information of the target object is calculated. Further, final positional information is obtained by synthesizing estimated positional information at a predetermined ratio, and the final positional information is output and fed back for a next estimation.