An ultrasound image diagnostic apparatus includes the following. An image generator generates tomographic image data of an object from generated acoustic ray data. A measuring target acknowledging unit acknowledges a measuring target of the object from the generated tomographic image data is stably drawn for a predetermined amount of time and when it is acknowledged, advances to a measuring performing mode of the measuring target. An initial condition obtaining unit obtains initial condition information for extracting an outline of the measuring target. An outline extractor uses the obtained initial condition information to extract an outline of the measuring target from the generated tomographic image data. A measuring unit obtains diameter information of the measuring target based on the extracted outline and calculates the feature amount of the measuring target from the diameter information.
