An image processing apparatus capable of displaying an image for providing guidance in moving an instrument to a target part in a subject to a user with high visual perceptibility. The image processing apparatus may be an ultrasound diagnostic apparatus including: a three-dimensional image analyzer determining target position indicating a three-dimensional position of the target part based on a three-dimensional image including the target part； a position information acquirer acquiring instrument position indicating a three-dimensional position of the instrument； a display state determiner selecting one display state from at least two display states, based on a positional relationship between the target part and the instrument； an assist image generator generating an assist image for the selected display state by using the target position and the instrument position； and a display controller performing control for outputting the assist image generated by the assist image generation unit to a display device.
