According to one embodiment, a system for diagnosing a pigmented lesion is provided. The system includes: a sound detector configured to detect a photoacoustic wave which is generated when a first laser is irradiated onto a target having a pigmented lesion; a disease diagnosis unit configured to determine a type of the pigmented lesion based on generated light which is generated when a second laser is irradiated onto the target; and a pigmented lesion diagnosis unit configured to calculate at least one of a depth and a thickness of the pigmented lesion based on a time at which the photoacoustic wave is detected and laser irradiation time information on the first laser irradiated onto the target.