An imaging system comprising: an imaging unit configured to image a subject including light emission patterns of chemiluminescent samples or fluorescent samples that attenuate with time; and a control unit configured to enable the imaging unit to perform pre-imaging one or more times, and main imaging one or more times following the pre-imaging; wherein the control unit has an image generating portion configured to generate a subject image for the pre-imaging based on one or more taken images in the pre-imaging and generates a subject image for the main imaging based on one or more taken images in the main imaging, an interface portion configured to display the subject image for the pre-imaging, a region setting portion configured to set a region-of-interest on a region of the subject image for the pre-imaging including light emission patterns of chemiluminescent samples or fluorescent samples and a non-region-of-interest of the subject image for the pre-imaging on a region of the subject image where light emission patterns of chemiluminescent samples or fluorescent samples are unlikely to be present, the imaging system characterized in that the control unit further has: a SN ratio calculating portion configured to calculate a signal-to-noise ratio, SN ratio (SN(t)), of the region-of-interest that changes according to a light exposure time (t), which is a ratio of a signal component of a pixel value to a noise component of the pixel value, based on pixel values within the set region-of-interest and pixel values within the set non-region-of-interest, and a total light exposure time calculating portion configured to calculate a total light exposure time in which a maximum SN ratio (SN 1) corresponding to a peak of the calculated SN ratio (SN(t)) or a preset reference SN ratio (SN 0) can be obtained, wherein the preset reference SN ratio is set as the product of a SN ratio calculated in the subject image for pre-imaging based on pixel values within the set region-of-interest and pixel values within the set non-region-of-interest and a reference SN ratio improvement coefficient that is set in advance; and wherein the control unit is configured to enable the imaging unit to perform the main imaging based on the total light exposure time. an imaging unit configured to image a subject including light emission patterns of chemiluminescent samples or fluorescent samples that attenuate with time; and a control unit configured to enable the imaging unit to perform pre-imaging one or more times, and main imaging one or more times following the pre-imaging; wherein the control unit has an image generating portion configured to generate a subject image for the pre-imaging based on one or more taken images in the pre-imaging and generates a subject image for the main imaging based on one or more taken images in the main imaging, an interface portion configured to display the subject image for the pre-imaging, a region setting portion configured to set a region-of-interest on a region of the subject image for the pre-imaging including light emission patterns of chemiluminescent samples or fluorescent samples and a non-region-of-interest of the subject image for the pre-imaging on a region of the subject image where light emission patterns of chemiluminescent samples or fluorescent samples are unlikely to be present, an image generating portion configured to generate a subject image for the pre-imaging based on one or more taken images in the pre-imaging and generates a subject image for the main imaging based on one or more taken images in the main imaging, an interface portion configured to display the subject image for the pre-imaging, a region setting portion configured to set a region-of-interest on a region of the subject image for the pre-imaging including light emission patterns of chemiluminescent samples or fluorescent samples and a non-region-of-interest of the subject image for the pre-imaging on a region of the subject image where light emission patterns of chemiluminescent samples or fluorescent samples are unlikely to be present, a SN ratio calculating portion configured to calculate a signal-to-noise ratio, SN ratio (SN(t)), of the region-of-interest that changes according to a light exposure time (t), which is a ratio of a signal component of a pixel value to a noise component of the pixel value, based on pixel values within the set region-of-interest and pixel values within the set non-region-of-interest, and a total light exposure time calculating portion configured to calculate a total light exposure time in which a maximum SN ratio (SN 1) corresponding to a peak of the calculated SN ratio (SN(t)) or a preset reference SN ratio (SN 0) can be obtained, wherein the preset reference SN ratio is set as the product of a SN ratio calculated in the subject image for pre-imaging based on pixel values within the set region-of-interest and pixel values within the set non-region-of-interest and a reference SN ratio improvement coefficient that is set in advance; and wherein the control unit is configured to enable the imaging unit to perform the main imaging based on the total light exposure time.