An endoscope system comprising: a plurality of semiconductor light sources (14, 20a-20d) configured to emit light having wavelength ranges different from each other; a light source control unit configured to perform control to cause the plurality of semiconductor light sources to emit a plurality of kinds of illumination light, which include first illumination light having a first light emission ratio and second illumination light having a second light emission ratio different from the first light emission ratio, while switching the plurality of kinds of illumination light according to a specific light emission order and a specific light emission period; an image acquisition unit configured to pick up images of an object to be observed illuminated with each illumination light to acquire a plurality of images, the plurality of images including first images obtained in a first observation mode using the first illumination light and second images obtained in a second observation mode using the second illumination light; a static-image-acquisition instruction input unit configured to give a static-image-acquisition instruction to acquire static images for storage of the respective images; a shake amount calculation section configured to calculate shake amounts of the plurality of images acquired in a specific static-image-acquisition instruction period (T p) including a timing when the static-image-acquisition instruction is given, wherein the shake amount calculation section is configured to perform different shake amount-calculation processing for calculating the shake amount depending on the observation mode in a case where an image, which is an object of which the shake amount is to be calculated, is acquired; and a static image-storage control section configured to perform control to store the plurality of images in a static image-storage unit as the static images for storage in a case where a specific condition is satisfied with regard to the shake amount; wherein the plurality of images are acquired as image sets in the specific static-image-acquisition instruction period, wherein the static image-storage control section stores an image set, which satisfies the specific condition, as the static images for storage; and wherein the image set satisfying the specific condition is an image set of which a representative shake amount, which is a sum of shake amounts of the respective images of the image set, is smallest among the plurality of image sets. a plurality of semiconductor light sources (14, 20a-20d) configured to emit light having wavelength ranges different from each other; a light source control unit configured to perform control to cause the plurality of semiconductor light sources to emit a plurality of kinds of illumination light, which include first illumination light having a first light emission ratio and second illumination light having a second light emission ratio different from the first light emission ratio, while switching the plurality of kinds of illumination light according to a specific light emission order and a specific light emission period; an image acquisition unit configured to pick up images of an object to be observed illuminated with each illumination light to acquire a plurality of images, the plurality of images including first images obtained in a first observation mode using the first illumination light and second images obtained in a second observation mode using the second illumination light; a static-image-acquisition instruction input unit configured to give a static-image-acquisition instruction to acquire static images for storage of the respective images; a shake amount calculation section configured to calculate shake amounts of the plurality of images acquired in a specific static-image-acquisition instruction period (T p) including a timing when the static-image-acquisition instruction is given, wherein the shake amount calculation section is configured to perform different shake amount-calculation processing for calculating the shake amount depending on the observation mode in a case where an image, which is an object of which the shake amount is to be calculated, is acquired; and a static image-storage control section configured to perform control to store the plurality of images in a static image-storage unit as the static images for storage in a case where a specific condition is satisfied with regard to the shake amount; wherein the plurality of images are acquired as image sets in the specific static-image-acquisition instruction period, wherein the static image-storage control section stores an image set, which satisfies the specific condition, as the static images for storage; and wherein the image set satisfying the specific condition is an image set of which a representative shake amount, which is a sum of shake amounts of the respective images of the image set, is smallest among the plurality of image sets.