An imaging apparatus comprising: a light source adapted to generate first light and second light, wherein the first light is pulsed light; an acoustic wave detector adapted to convert an acoustic wave generated from a light absorption material in an object which has absorbed a part of energy of the first light generated from said light source to said object, into a first electric signal; a photodetector adapted to convert an optical intensity of the second light that is generated from said light source and has propagated in said object or an optical intensity of third light having a wavelength different from that of the second light and which is emitted from the light absorption material due to absorption of a part of the energy of the second light irradiated from the light source to the object, into a second electric signal; a calculation unit adapted to calculate, using the first electric signal, an optical energy absorption density distribution (μ a ·Φ) in said object and an information on a size and a location of the light absorption material, characterized in that the calculation unit is adapted to: calculate, using the second electric signal and the information on the size and the location of the light absorption material, a light amount distribution of the first light (Φ) in said object, and calculate, using the optical energy absorption density distribution (μ a ·Φ) and the light amount distribution of the first light (Φ), an absorption coefficient distribution (μ a) in said object. a light source adapted to generate first light and second light, wherein the first light is pulsed light; an acoustic wave detector adapted to convert an acoustic wave generated from a light absorption material in an object which has absorbed a part of energy of the first light generated from said light source to said object, into a first electric signal; a photodetector adapted to convert an optical intensity of the second light that is generated from said light source and has propagated in said object or an optical intensity of third light having a wavelength different from that of the second light and which is emitted from the light absorption material due to absorption of a part of the energy of the second light irradiated from the light source to the object, into a second electric signal; a calculation unit adapted to calculate, using the first electric signal, an optical energy absorption density distribution (μ a ·Φ) in said object and an information on a size and a location of the light absorption material, characterized in that the calculation unit is adapted to: calculate, using the second electric signal and the information on the size and the location of the light absorption material, a light amount distribution of the first light (Φ) in said object, and calculate, using the optical energy absorption density distribution (μ a ·Φ) and the light amount distribution of the first light (Φ), an absorption coefficient distribution (μ a) in said object. calculate, using the second electric signal and the information on the size and the location of the light absorption material, a light amount distribution of the first light (Φ) in said object, and calculate, using the optical energy absorption density distribution (μ a ·Φ) and the light amount distribution of the first light (Φ), an absorption coefficient distribution (μ a) in said object.