An information processing device for obtaining positional information of a target object having a plurality of markers, the information processing device comprising: a marker position obtaining section configured to extract images of the markers from a photographed image obtained by photographing the target object, and obtain position coordinates of representative points of the markers in a three-dimensional space; a target point position calculating section configured to obtain position coordinates of the target object using the position coordinates of the representative point of each of the markers; a position estimating section configured to estimate the position coordinates of the target object on a basis of an output value of a sensor included in the target object; a filtering section configured to determine final position coordinates (Position out ) of the target object by synthesizing, at a predetermined synthesizing ratio (k), the obtained position coordinates (Position image ) of the target object, the obtained position coordinates (Position image ) being obtained by the target point position calculating section, and the estimated position coordinates (Position sensor ) of the target object, the estimated position coordinates (Position sensor ) being estimated by the position estimating section, and output the final position coordinates (Position out ) of the target object; and a weight adjusting section configured to determine a weight coefficient for each of the markers on a basis of a parameter corresponding to an area of an image of the marker on a model, the image being formed by projecting a target object model of the target object disposed in a virtual three-dimensional space onto an imaging plane and an angle between the marker in the target object model and the imaging plane, wherein the target point position calculating section calculates the position coordinates of the target object after applying the weight coefficient to the position coordinates of the representative point of each of the markers. a marker position obtaining section configured to extract images of the markers from a photographed image obtained by photographing the target object, and obtain position coordinates of representative points of the markers in a three-dimensional space; a target point position calculating section configured to obtain position coordinates of the target object using the position coordinates of the representative point of each of the markers; a position estimating section configured to estimate the position coordinates of the target object on a basis of an output value of a sensor included in the target object; a filtering section configured to determine final position coordinates (Position out ) of the target object by synthesizing, at a predetermined synthesizing ratio (k), the obtained position coordinates (Position image ) of the target object, the obtained position coordinates (Position image ) being obtained by the target point position calculating section, and the estimated position coordinates (Position sensor ) of the target object, the estimated position coordinates (Position sensor ) being estimated by the position estimating section, and output the final position coordinates (Position out ) of the target object; and a weight adjusting section configured to determine a weight coefficient for each of the markers on a basis of a parameter corresponding to an area of an image of the marker on a model, the image being formed by projecting a target object model of the target object disposed in a virtual three-dimensional space onto an imaging plane and an angle between the marker in the target object model and the imaging plane, wherein the target point position calculating section calculates the position coordinates of the target object after applying the weight coefficient to the position coordinates of the representative point of each of the markers. <EOS>