A three-dimensional ultrasonic image with which the positional relationship between tissues can be surely grasped is generated. Accordingly, an ultrasonic imaging apparatus and a projection image generating method according to the present invention acquire first three-dimensional image data and second three-dimensional image data, generate a first projection image on the basis of at least a part of the first three-dimensional image data and the second three-dimensional image data, and generate a second projection image on the basis of at least a part of the second three-dimensional image data and the first three-dimensional imaged data.
