A lower eyelid detection device (10, 10A), comprising: an extractor (21, 20b) using an edge detection operator for calculating an edge value for each of pixels constituting an image of eyes (51, 52) of a driver, and extracting, from the pixels, pixels having an edge value equal to or more than a first threshold or having an edge value equal to or less than a second threshold as edge pixels; and a calculator (21, 20c, 20e) for detecting a lower eyelid of the driver by calculating an evaluation value of adjacent edge pixels in a first direction while scanning the image in a second direction perpendicular to the first direction, thereby using a lower eyelid search window that extends in the first direction and is one pixel wide in the second direction, the evaluation value being determined based on a value of the total of edge values of the edge pixels overlapped by the lower eyelid search window, wherein the calculator is configured to detect the position of the lower eyelid search window where the evaluation value is minimized as the position of the lower eyelid, wherein at said position, the lower eyelid search window overlaps a first group of the edge pixels arranged in the first direction, characterized by: a transformer (21, 20f) for transforming the lower eyelid search window at the position where the evaluation value is minimized to increase the evaluation value by scanning a pixel search window (W3, W4) having a dimension of one pixel in the first direction and a dimension of three pixels in the second direction and being positioned at the end of the first group of edge pixels, wherein the pixel search window (W3, W4) is moved in the first direction thereby overlapping with pixels at positions shifted from the first group of edge pixels by one pixel in the second direction, thereby extracting a second group of edge pixels arranged in the first direction and shifted from the first group of edge pixels in the second direction, and transforming the lower eyelid search window so that the transformed lower eyelid search window overlaps with the first and second groups of edge pixels, repeating the transformation by scanning with the search window (W3, W4) starting from the end of the second group of edge pixels to extract further groups of edge pixels as parts of the lower eyelid; and a setter (21, 20g) for setting the reference position of the eyelid to a centroid or a center of the transformed lower eyelid search window. an extractor (21, 20b) using an edge detection operator for calculating an edge value for each of pixels constituting an image of eyes (51, 52) of a driver, and extracting, from the pixels, pixels having an edge value equal to or more than a first threshold or having an edge value equal to or less than a second threshold as edge pixels; and a calculator (21, 20c, 20e) for detecting a lower eyelid of the driver by calculating an evaluation value of adjacent edge pixels in a first direction while scanning the image in a second direction perpendicular to the first direction, thereby using a lower eyelid search window that extends in the first direction and is one pixel wide in the second direction, the evaluation value being determined based on a value of the total of edge values of the edge pixels overlapped by the lower eyelid search window, wherein the calculator is configured to detect the position of the lower eyelid search window where the evaluation value is minimized as the position of the lower eyelid, wherein at said position, the lower eyelid search window overlaps a first group of the edge pixels arranged in the first direction, a transformer (21, 20f) for transforming the lower eyelid search window at the position where the evaluation value is minimized to increase the evaluation value by scanning a pixel search window (W3, W4) having a dimension of one pixel in the first direction and a dimension of three pixels in the second direction and being positioned at the end of the first group of edge pixels, wherein the pixel search window (W3, W4) is moved in the first direction thereby overlapping with pixels at positions shifted from the first group of edge pixels by one pixel in the second direction, thereby extracting a second group of edge pixels arranged in the first direction and shifted from the first group of edge pixels in the second direction, and transforming the lower eyelid search window so that the transformed lower eyelid search window overlaps with the first and second groups of edge pixels, repeating the transformation by scanning with the search window (W3, W4) starting from the end of the second group of edge pixels to extract further groups of edge pixels as parts of the lower eyelid; and a setter (21, 20g) for setting the reference position of the eyelid to a centroid or a center of the transformed lower eyelid search window.