A position/orientation estimation apparatus configured to estimate a position and an orientation of an object, the position/orientation estimation apparatus comprising: a first acquisition unit configured to acquire a two-dimensional image of the object; a second acquisition unit configured to acquire a three-dimensional model expressing a three-dimensional shape of the object; and a third acquisition unit configured to acquire position/orientation information expressing pre-update position and orientation of the object that are estimated; a second position/orientation estimation unit configured to update the position/orientation information with regard to a translation in an X-axis and a translation in a Y-axis, which are two different axes on a plane of the two-dimensional image, and a rotation about a Z-axis that is orthogonal to the X-axis and the Y-axis, using the three-dimensional model and the two-dimensional image; and an output unit configured to output the position and the orientation expressed by the updated position/orientation information as the position and the orientation of the object, wherein the second position/orientation estimation unit includes: a two-dimensional model generation unit (step S200) configured to generate a two-dimensional model projected on the same plane as that of the two-dimensional image, based on the position/orientation information, an optimization unit (step S220) configured to optimize a translation parameter in the X-axis, a translation parameter in the Y-axis, and a rotation parameter about the Z-axis by matching the positions of the two-dimensional image and the two-dimensional model; and an updating unit (step S240) configured to update the position/orientation information using the optimized three parameters. a first acquisition unit configured to acquire a two-dimensional image of the object; a second acquisition unit configured to acquire a three-dimensional model expressing a three-dimensional shape of the object; and a third acquisition unit configured to acquire position/orientation information expressing pre-update position and orientation of the object that are estimated; a second position/orientation estimation unit configured to update the position/orientation information with regard to a translation in an X-axis and a translation in a Y-axis, which are two different axes on a plane of the two-dimensional image, and a rotation about a Z-axis that is orthogonal to the X-axis and the Y-axis, using the three-dimensional model and the two-dimensional image; and an output unit configured to output the position and the orientation expressed by the updated position/orientation information as the position and the orientation of the object, wherein the second position/orientation estimation unit includes: a two-dimensional model generation unit (step S200) configured to generate a two-dimensional model projected on the same plane as that of the two-dimensional image, based on the position/orientation information, an optimization unit (step S220) configured to optimize a translation parameter in the X-axis, a translation parameter in the Y-axis, and a rotation parameter about the Z-axis by matching the positions of the two-dimensional image and the two-dimensional model; and an updating unit (step S240) configured to update the position/orientation information using the optimized three parameters. a two-dimensional model generation unit (step S200) configured to generate a two-dimensional model projected on the same plane as that of the two-dimensional image, based on the position/orientation information, an optimization unit (step S220) configured to optimize a translation parameter in the X-axis, a translation parameter in the Y-axis, and a rotation parameter about the Z-axis by matching the positions of the two-dimensional image and the two-dimensional model; and an updating unit (step S240) configured to update the position/orientation information using the optimized three parameters.