A subject tracking computer program product containing a subject tracking program executed by a computer in order to track movement of a subject through a plurality of input images input in time series. The subject tracking program enables the computer to execute: a template matching step through which each input image is matched with a plurality of template images at various magnification factors through template matching, a template image among the plurality of template images achieving a highest level of similarity to an image within a specific area in the input image is selected as a chosen template image and the specific are in the input image is extracted as a match-up are; a decision step through which a decision is made as to whether or not matching results obtained through the template matching step satisfy an update condition for updating the plurality of template images; and an update step through which at least one of the plurality of template images is updated upon deciding through the decision step that the update condition is satisfied.