There is used an object information acquiring apparatus including a probe for electrically scanning an object in first direction and mechanically scanning in second direction intersecting with the first direction, a first delay-and-sum unit for operating a delay-and-sum on a received signal, a memory for storing a first delay-and-sum signal for each plane in the second direction, a selecting unit for selecting signals corresponding to M sectional planes from among the stored signals, a second delay-and-sum unit for operating a delay-and-sum on the selected signals in the second direction, and a unit for acquiring image in the object from the second delay-and-sum signal, the second delay-and-sum unit switching, according to the mechanical scanning, a first case in which M signals are fixed and a delay pattern is varied and a second case in which a set of the M signals is varied and the delay pattern is fixed.
