Image acquisition device and image acquisition method for image acquisition device

In an image acquisition device, imaging is performed using an imaging element capable of rolling reading an optical image of a sample irradiated with instantaneous light. Therefore, the image can be captured with a sufficient S/N ratio even when the optical image is weak. Further, the image acquisition device includes a light source control unit that causes the instantaneous light to be emitted from a light source from the start of exposure of a pixel row of which reading last starts to the start of reading of a pixel row of which the reading first starts. That is, in the image acquisition device, the light source control unit causes the sample to be irradiated with the instantaneous light from the light emitting means during a period of time in which all pixel rows of the imaging element are exposed.