1. A medical image diagnostic apparatus comprising: an image display that displays a medical image including a target part of an object; an input device that enables a user to input a type and feature points of the target part; and a processor, the processor comprising a control unit, the control unit configured to control: a contour model specifying unit for specifying a contour model, which is stored in a first storage unit, based on the type of the target part; a contour position estimator that estimates a contour position of the target part to generate an initial contour by adjusting a shape information of a contour model data, which is specified by the contour model specifying unit, in accordance with positions of the feature points; and a contour extractor that extracts a contour along a shape of the target part by fitting the initial contour to a contour of the target part with moving an edge of the initial contour to a wall surface of the contour of the target part, along with moving feature points of the initial contour towards a location of the feature points of the target part; wherein a shape of the initial contour is expressed by a first group of positions placed on a curve line and a second group of positions corresponding to the feature points of the initial contour, and when the contour extractor extracts the contour, the shape of the initial contour changes by moving the first group of positions closer to the wall surface of myocardium, using a boundary detection processing, and by moving the second group of positions in a direction towards the feature points of the target part, such that the extracted contour passes through the feature points of the target part, wherein the feature points of the initial contour are different than the feature points of the target part; and wherein the control unit is further configured to display a composite image that is obtained by combining the extracted contour and the medical image, on the image display.