This photoacoustic imager (100, 200, 300, 400, 500, 600) includes a light source portion (11, 211, 511, 611) and a detection portion(12), and is configured to set pulsed light emitted by the light source portion to a pulse width tw expressed in the following expression, assuming that fmax represents the maximum frequency of an acoustic wave A detected by the detection portion: 0.5/fmax≤tw≤1/fmax
