This paper presents a fast pose estimation algorithm of a 3D free form object in 2D images using 2D distance maps. One of the popular techniques of the pose estimation of 3D object in 2D image is the point-based method such as the ICP algorithm. However, the calculation cost for determining point correspondences is expensive. To overcome this problem, the proposed method utilizes a distance map on the 2D image plane, which is constructed quite rapidly by the fast marching method. For pose estimation of the object, contour lines of the 2D image and the projection of the 3D object are aligned using the distance map iteratively by the robust m-estimator. Some experimental results with simulated models and actual images of the endoscopic operation are successfully carried out.