To provide an image signal processing device capable of correcting an image having unevenness in luminance without shifting the temporal position of the image.

A summation unit 11 calculates a sum of pixels on each line of an image signal. A storage unit 12 stores the sum by an amount equal to the number of lines in a vertical valid image period. A determination unit 15 compares the sum on a line of interest of a frame of interest and the sum of the same line of interest of a past frame read out from the storage unit 12 and thereby determines a degree of change in luminance. A correction coefficient generation unit 152 generates a correction coefficient for correcting the image signal if the degree of change in luminance exceeds a prescribed threshold. A write control unit 151 exerts control so that the sum is stored by the storage unit 12 only when the degree of change in luminance is equal to or less than the prescribed threshold. A multiplication unit 16 multiplies the image signal delayed by a storage unit 13 by the correction coefficient before the image signal is output.