PROBLEM TO BE SOLVED: To provide an image processing apparatus and a medical image diagnostic apparatus capable of improving accuracy of detecting linear signals included in an image.SOLUTION: The image processing apparatus comprises a data acquisition unit 151 and a signal detection unit 152. The data acquisition unit 151 acquires image data, and the signal detection unit 152 detects linear signals included in the image by a signal detection area including detection ranges independent from each other at both ends in a longitudinal direction.