PROBLEM TO BE SOLVED: To provide a color tone adjusting device for keeping the color tone of an image to be picked up at a constant level, irrespective of a secular change of spectrum distribution of an illumination light.SOLUTION: The light from a light source 21 is irradiated via a light guide 22 and an image is picked up using an image pickup element 14. A white plate 24 is irradiated with the light from a branch fiber bundle 22A of the light guide 22 and a light reflected on the plate 24 is picked up using a second image pickup element 32. RGB signals obtained in advance by picking up the white plate 24 by the first and second image pickup elements 14, 32 under the same illumination condition are stored in a memory 34 as a first RGB signal and a second RGB signal, respectively. A first gain for correcting the difference in the spectrum sensitivity distribution between the first and second image pickup elements 14, 32 is calculated from the first and second RGB signals. A second gain for correcting a change in spectrum distribution of an illumination light is calculated from the first and second RGB signals detected by the second image pickup element 32. The gain of an RGB signal from the image pickup element 14 is adjusted on the basis of the first and second gains in a front stage video signal processing circuit 18.
