1. A medical diagnostic imaging apparatus, comprising: an image data acquiring unit for acquiring a plurality of images of a moving organ of a test object that moves periodically; a display unit for displaying the images acquired by the image data acquiring unit; a matching computation unit for performing a matching computation between a template extracted containing a tracking point on one image and another image; a template extracting unit for extracting, from the other image, a region correlated with the template as a template of the other image by the matching computation; a storing unit for correlating the template with a time phase at which it has been extracted and storing the template therein; and a control unit for controlling each of the units, the medical diagnostic imaging apparatus being for tracking a movement of the tracking point based on the extracted template, wherein the template extracting unit extracts, as a key template, a region containing one or more tracking points set on an image at least one selected time phase of the moving organ, and wherein the matching computation unit performs the matching computation using the key template in the vicinity of the time phase at which the key template is extracted.