An image processing apparatus generates intermediate volume data from a plurality of volume data segments obtained as time passes so as to implement high-speed volume data. A medical imaging apparatus that includes the image processing apparatus, an ultrasonic imaging apparatus, an image processing method, and a medical image generation method are disclosed. The image processing apparatus includes a displacement vector generator configured to detect corresponding voxels between reference volume data and target volume data that has been acquired at intervals of a predetermined time period, and to generate a displacement vector between the corresponding voxels; and an intermediate volume data generator configured to generate at least one piece of intermediate volume data between the reference volume data and the target volume data by using the generated displacement vector.