An eye opening degree detection system comprising: a plurality of imaging devices that generates images including, at least, regions of both eyes of a target person while shifting time; a one eye opening degree calculation unit that calculates each one eye opening degree of the left and right eyes of a first image; an eye opening degree selection unit that creates a pixel brightness value histogram of each region of the left and right eyes when the left and right one eye opening degrees do not substantially match each other, and selects a correctly-calculated one eye opening degree on the basis of the pixel brightness value histogram; an eye opening degree calculation unit that calculates an eye opening degree on the basis of the left and right one eye opening degrees when the left and right one eye opening degrees substantially match each other, and calculates an eye opening degree on the basis of the one eye opening degree selected by the eye opening degree selection unit when the left and right one eye opening degrees do not substantially match each other; and an eye opening degree detection device having an eye opening degree determination unit that compares the eye opening degree calculated on the basis of the first image with an eye opening degree calculated on the basis of a second image prior to the first image to determine the propriety of the eye opening degree calculated on the basis of the first image wherein the eye opening degree determination unit determines that the eye opening degree calculated on the basis of the first image is valid when a difference between the eye opening degree calculated on the basis of the first image and the eye opening degree calculated on the basis of the second image is equal to or smaller than a threshold value calculated on the basis of an imaging timing difference between the first image and the second image, wherein said threshold is proportional to the ratio of the imaging timing difference between said first and second imaging devices and half of the blink speed. a plurality of imaging devices that generates images including, at least, regions of both eyes of a target person while shifting time; a one eye opening degree calculation unit that calculates each one eye opening degree of the left and right eyes of a first image; an eye opening degree selection unit that creates a pixel brightness value histogram of each region of the left and right eyes when the left and right one eye opening degrees do not substantially match each other, and selects a correctly-calculated one eye opening degree on the basis of the pixel brightness value histogram; an eye opening degree calculation unit that calculates an eye opening degree on the basis of the left and right one eye opening degrees when the left and right one eye opening degrees substantially match each other, and calculates an eye opening degree on the basis of the one eye opening degree selected by the eye opening degree selection unit when the left and right one eye opening degrees do not substantially match each other; and an eye opening degree detection device having an eye opening degree determination unit that compares the eye opening degree calculated on the basis of the first image with an eye opening degree calculated on the basis of a second image prior to the first image to determine the propriety of the eye opening degree calculated on the basis of the first image wherein the eye opening degree determination unit determines that the eye opening degree calculated on the basis of the first image is valid when a difference between the eye opening degree calculated on the basis of the first image and the eye opening degree calculated on the basis of the second image is equal to or smaller than a threshold value calculated on the basis of an imaging timing difference between the first image and the second image, wherein said threshold is proportional to the ratio of the imaging timing difference between said first and second imaging devices and half of the blink speed.