1. A position and orientation measurement apparatus comprising: a storage unit adapted to store information of a three-dimensional shape model of a target object; a distance information obtaining unit adapted to obtain distance information of the target object captured by a capturing unit; a grayscale image obtaining unit adapted to obtain a grayscale image of the target object captured by the capturing unit; a first position and orientation estimation unit adapted to estimate a first estimated value representative of the position and orientation of the target object based on the information of the three-dimensional shape model stored in said storage unit and the distance information; a second position and orientation estimation unit adapted to estimate a second estimated value representative of the position and orientation of the target object based on a geometric feature of the grayscale image and projection information obtained by projecting, on the grayscale image, the information of the three-dimensional shape model stored in said storage unit; and a determination unit adapted to determine whether a parameter of the capturing unit is needed to be calibrated or not, based on both the first estimated value estimated by said first position and orientation estimation unit and the second estimated value estimated by said second position and orientation estimation unit.