First, the data of a moving image that is captured is read for each frame, and whether to start tracking is determined based on the presence or absence of a target object (S20, S22). An edge image of the image frame is created after it is determined to start tracking (S24). Meanwhile, a particle is distributed in a space of a coefficient set for each control point sequence when the control point sequence of a B-spline curve representing the shape of the target object is represented in a linear combination of control point sequence of a B-spline curve representing a plurality of reference shapes that are made available in advance (S26). A particle is also distributed in the space of a shape-space vector (S28), the likelihood of each particle is observed, and the probability density distribution is acquired (S30). A curve obtained by weighting parameters by the probability density distribution and then averaging the weighted parameters is created as a tracking result (S32).