A photoacoustic (PA) apparatus and a method of operating the same are provided. The method includes: irradiating a laser beam onto a region of interest (ROI) which includes a flow and receiving a first PA signal corresponding to the irradiated laser beam generating a first PA image on the basis of the first PA signal irradiating a laser beam onto the ROI where the flow is restricted and receiving a second PA signal corresponding to the irradiated laser beam generating a second PA image on the basis of the second PA signal generating a difference image between the first PA image and the second PA image and displaying the difference image.
