An X-ray image acquisition device includes a pixel unit having M pixel arrays each including N pixel portions (N and M are integers of 2 or more), M circuit units, and a control unit. Each circuit unit includes T (T is an integer of N or more) adding sections that sequentially add electrical signals corresponding to output signals from the N pixel portions and a switch section for switching connection states between the N pixel portions and the T adding sections. The control unit switches the connection states in synchronization with the transportation of an object along a first direction so that the electrical signals corresponding to the output signals output from the pixel portions by detecting X-rays transmitted through the same region of the object are added by the same adding sections.