1. An image acquisition apparatus comprising: an imaging device on which images of a plurality of small areas allocated to an area to be imaged are formed; a processor; and a memory device storing instructions, which when executed by the processor, cause the processor to: (a) detect intensity of light irradiated on the small area from a light source; (b) integrate the detected intensity of light; (c) if an integration value of the integrated intensity of light from a point in time when light is emitted from the light source is greater than a predetermined threshold value, terminate emission of light from the light source; (d) start exposure of the imaging device before light is emitted from the light source; (e) terminate exposure of the imaging device after emission of light from the light source is terminated; and (f) repeat steps (a) to (e) for the small areas to acquire the images of the small areas as a divided image from the imaging device, wherein each of the small areas are illuminated by the same amount of light.