It is expected that the use of haptic sensors to measure the magnitude, direction, and distribution of a force will enable a robotic hand to perform dexterous manipulations. Therefore, we have developed a new type of finger-shaped haptic sensor that can measure a three-dimensional force vector field over a contact surface. The sensor consists of a transparent elastic body, two layers of internal blue and red markers, and a CCD camera to capture the movements of the markers. Using the elastic theory, we can calculate the force vector field from the captured movements of the markers. However, the elastic theory cannot be applied to the finger-shaped sensor because of its complicated shape. Therefore, we use actual measurements for the calibration in order to develop a prototype of the sensor. Then, we evaluate its basic performance. The result shows that the sensor performance can be improved further, and the sensor can be successfully used in a robotic hand.