A photoacoustic imaging apparatus includes a detector that outputs detection signals by detecting acoustic waves generated at surfaces and an inner portion of a sample by irradiating the sample with light and a signal processing unit that generates image data using the detection signal. The signal processing unit calculates an average sound speed in the inner portion of the sample by using the detection signal of the acoustic wave generated at the surface of the sample and propagated through the inner portion of the sample, and generates the image data using the average sound speed and the detection signal of the acoustic wave generated at the inner portion of the sample.
