An endoscope system comprising: an endoscope having disposed in a tip portion thereof an imaging element that performs imaging of an observation target and outputs a medical image; a medical image acquisition unit that acquires the medical image; a region-of-interest detection unit that detects a region of interest located in a first part to be observed within the observation target from a medical image acquired at a first timing; a first determination unit that performs first determination processing for determining, in a case where the tip portion moves away from the first part to be observed and moves toward a second part to be observed different from the first part to be observed, and then the tip portion moves away from the second part to be observed and moves toward the first part to be observed, whether the tip portion has returned to the first part to be observed, by using a medical image acquired at a second timing different from the first timing; a display control unit that performs display control of a display unit by using a determination result of the first determination unit; and a second determination unit that performs second determination processing for determining whether the region of interest in the first part to be observed is overlooked, wherein the display control unit performs the display control by using the determination result of the first determination unit and a determination result of the second determination unit, and wherein the second determination unit performs the second determination processing by using a first time period indicating a time period from when the region of interest in the first part to be observed is detected to when the region of interest disappears from the display unit and by using a second time period indicating a time period that begins after the region of interest disappears from the display, and wherein the second determination unit determines that the region of interest in the first part to be observed is overlooked when the first time period is shorter than a second-determination first time period and the second time period is longer than or equal to a second-determination second time period. an endoscope having disposed in a tip portion thereof an imaging element that performs imaging of an observation target and outputs a medical image; a medical image acquisition unit that acquires the medical image; a region-of-interest detection unit that detects a region of interest located in a first part to be observed within the observation target from a medical image acquired at a first timing; a first determination unit that performs first determination processing for determining, in a case where the tip portion moves away from the first part to be observed and moves toward a second part to be observed different from the first part to be observed, and then the tip portion moves away from the second part to be observed and moves toward the first part to be observed, whether the tip portion has returned to the first part to be observed, by using a medical image acquired at a second timing different from the first timing; a display control unit that performs display control of a display unit by using a determination result of the first determination unit; and a second determination unit that performs second determination processing for determining whether the region of interest in the first part to be observed is overlooked, wherein the display control unit performs the display control by using the determination result of the first determination unit and a determination result of the second determination unit, and wherein the second determination unit performs the second determination processing by using a first time period indicating a time period from when the region of interest in the first part to be observed is detected to when the region of interest disappears from the display unit and by using a second time period indicating a time period that begins after the region of interest disappears from the display, and wherein the second determination unit determines that the region of interest in the first part to be observed is overlooked when the first time period is shorter than a second-determination first time period and the second time period is longer than or equal to a second-determination second time period.