An image acquisition apparatus comprising: a movable stage for placing a biological sample thereon; an imaging device on which an image of a small area of the biological sample among a plurality of small areas can be formed thereon, the plurality of small areas being allocated areas of an area to be imaged of the biological sample, wherein the movable stage is adapted to be moved such that small areas are imaged sequentially; a light source unit and an optical system being arranged on different sides of a plane of the movable stage, wherein the light source unit comprises a light source, a condenser and a detection section; wherein the detection section is adapted to detect intensity of light emitted by the light source, and wherein the detection section is disposed at a position between the light source and the condenser such that it is irradiated by a part of diffused light and without blocking a light path of light irradiated on the condenser for further irradiating the biological sample; an integration section being adapted to integrate the intensity of light detected by the detection section and sent to the integrator as a light-intensity signal; a light-source control section that is adapted to terminate emission of light from the light source if an integration value of the intensity of light integrated by the integration section from a point in time when light is emitted from the light source is greater than a predetermined threshold value,; an exposure control section adapted to start exposure of the imaging device before light is emitted from the light source and to terminate exposure of the imaging device after emission of light from the light source is terminated; and an image acquisition section adapted to acquire the image of the small area from the imaging device, and an image correction section adapted to correct luminance values of the small area images so that the integration values become constant. a movable stage for placing a biological sample thereon; an imaging device on which an image of a small area of the biological sample among a plurality of small areas can be formed thereon, the plurality of small areas being allocated areas of an area to be imaged of the biological sample, wherein the movable stage is adapted to be moved such that small areas are imaged sequentially; a light source unit and an optical system being arranged on different sides of a plane of the movable stage, wherein the light source unit comprises a light source, a condenser and a detection section; wherein the detection section is adapted to detect intensity of light emitted by the light source, and wherein the detection section is disposed at a position between the light source and the condenser such that it is irradiated by a part of diffused light and without blocking a light path of light irradiated on the condenser for further irradiating the biological sample; an integration section being adapted to integrate the intensity of light detected by the detection section and sent to the integrator as a light-intensity signal; a light-source control section that is adapted to terminate emission of light from the light source if an integration value of the intensity of light integrated by the integration section from a point in time when light is emitted from the light source is greater than a predetermined threshold value,; an exposure control section adapted to start exposure of the imaging device before light is emitted from the light source and to terminate exposure of the imaging device after emission of light from the light source is terminated; and an image acquisition section adapted to acquire the image of the small area from the imaging device, and an image correction section adapted to correct luminance values of the small area images so that the integration values become constant.