Gain adjustment unit, recording medium holding gain adjustment program, endoscope and endoscope apparatus

A recording medium holding a gain adjustment program, the gain adjustment program causing a computer to execute:

• a step of calculating a total sum of analog gains on a way from photoelectric conversion output of an image pickup device to input of an analog/digital conversion circuit with use of a picked-up image based on an output of the image pickup device at bright time and a picked-up image based on an output of the image pickup device at dark time among picked-up images provided from the analog/digital conversion circuit, the analog/digital conversion circuit being configured to convert an output of an analog processing section into a digital signal, the analog processing section being configured to transmit and amplify an image pickup signal from the image pickup device, the image pickup device being provided at an insertion portion of an endoscope;
• and
• a step of determining, as an adjustment gain, a difference between a target value of a total sum of gains on the way from the photoelectric conversion output of the image pickup device to the input of the analog/digital conversion circuit and the total sum of the analog gains, and outputting information of the adjustment gain to adjust an analog gain of the endoscope.