An object information acquiring apparatus, comprising: a light source; an acoustic wave detector having, disposed on a reception surface thereof, a two-dimensional array including a plurality of elements configured to detect acoustic waves generated by an object corresponding to a reconstruction area at which image reconstruction is performed, the acoustic waves were induced by irradiation of the object with light from the light source; an acoustic signal generator configured to generate acoustic signals used in image reconstruction, from the acoustic waves detected by the acoustic wave detector; an element selector configured to select elements that are used in image reconstruction from among the plurality of elements of the array; a reconstructor configured to perform 3D image reconstruction to generate an image data of a point of interest within the reconstruction area using acoustic signals based on the acoustic waves detected by the elements selected by the element selector, and a position controller configured to move the acoustic wave detector, wherein the element selector is configured to calculate an effective area of the array for the point of interest, said effective area comprising elements of the array such that the point of interest is contained within the directionality range of said elements and further to select elements among the elements of the effective area in such a manner that, for each selected element, there exists another selected element located at a symmetrical position with respect to a point at which the reception surface is intersected by a perpendicular line drawn from the point of interest to the reception surface and said another selected element is further located within the effective area, while omitting an element that lies within the effective area but that has no symmetrically-positioned element within the effective area, wherein, the element selector is configured to select virtual elements from among a virtual element group of a virtual reception area that combines the reception surface of the acoustic wave detector at each position to which the acoustic wave detector is moved and the effective area of the array comprises virtual elements such that the point of interest is contained within the directionality range of said virtual elements, and wherein the reconstructor is configured to perform image reconstruction using acoustic signals detected by the virtual elements selected by the element selector, the virtual elements are configured to be symmetrically positioned within the effective area on the virtual reception area with respect to a point where a line perpendicular to the array and extending from the point of interest intersects the virtual reception area. a light source; an acoustic wave detector having, disposed on a reception surface thereof, a two-dimensional array including a plurality of elements configured to detect acoustic waves generated by an object corresponding to a reconstruction area at which image reconstruction is performed, the acoustic waves were induced by irradiation of the object with light from the light source; an acoustic signal generator configured to generate acoustic signals used in image reconstruction, from the acoustic waves detected by the acoustic wave detector; an element selector configured to select elements that are used in image reconstruction from among the plurality of elements of the array; a reconstructor configured to perform 3D image reconstruction to generate an image data of a point of interest within the reconstruction area using acoustic signals based on the acoustic waves detected by the elements selected by the element selector, and a position controller configured to move the acoustic wave detector, wherein the element selector is configured to calculate an effective area of the array for the point of interest, said effective area comprising elements of the array such that the point of interest is contained within the directionality range of said elements and further to select elements among the elements of the effective area in such a manner that, for each selected element, there exists another selected element located at a symmetrical position with respect to a point at which the reception surface is intersected by a perpendicular line drawn from the point of interest to the reception surface and said another selected element is further located within the effective area, while omitting an element that lies within the effective area but that has no symmetrically-positioned element within the effective area, wherein, the element selector is configured to select virtual elements from among a virtual element group of a virtual reception area that combines the reception surface of the acoustic wave detector at each position to which the acoustic wave detector is moved and the effective area of the array comprises virtual elements such that the point of interest is contained within the directionality range of said virtual elements, and wherein the reconstructor is configured to perform image reconstruction using acoustic signals detected by the virtual elements selected by the element selector, the virtual elements are configured to be symmetrically positioned within the effective area on the virtual reception area with respect to a point where a line perpendicular to the array and extending from the point of interest intersects the virtual reception area.