An object information acquiring apparatus, comprises an irradiation unit configured to irradiate light from a light source onto a breast, which is an object a detection unit configured to detect a signal propagating from the breast by the light irradiated from the irradiation unit a calculation unit configured to calculate an optical characteristic inside the breast based on the signal detected by the detection unit, wherein the irradiation unit configured to irradiate the light onto the breast in a direction away from a chest wall located at the base of the breast.
