An imaging apparatus is disclosed for diagnosis including a plurality of transmitting and receiving units, an error of a scale of a tomographic image to be generated is reduced. The imaging apparatus can include including acquisition means for acquiring a propagation velocity of an ultrasound signal of a flushing liquid, generation means for generating ultrasound line data based on the propagation velocity of the ultrasound signal in a blood vessel tissue, and conversion means for converting positional information of each position within a range in which the flushing liquid flows regarding the ultrasound line data generated by the generation means based on a ratio between the propagation velocity in the blood vessel tissue and the propagation velocity in the flushing liquid. A tomographic image of a blood vessel is constructed by using the ultrasound line data converted by the conversion means.