1. A medical image diagnostic apparatus comprising: an image display unit that displays a medical image including a target part of an object; an input unit that inputs feature points of the target part; a contour position estimation unit that estimates a contour position of the target part to generate an initial contour; a contour extraction unit that extracts a contour along a shape of the target part using the feature points and the initial contour; and a control unit that displays a composite image, which is obtained by combining the extracted contour and the medical image, on the image display unit.