An object information acquiring apparatus includes: a receiving element configured to receive an acoustic wave generated by emission of light from a light source on an object and output an electric signal; an amplifying unit configured to amplify the electric signal; a scanning unit configured to move relative positions of the receiving element and the object; a controlling unit configured to determine a gain of the amplifying unit according to time when the receiving element receives the acoustic wave; and a processing unit configured to acquire characteristics information on the object, using the electric signal. The controlling unit determines the gain of the amplifying unit according to a positional relation between the receiving element and the object.