To minimize image acquisition time and to apply an image sensor to a mobile subject distance measuring equipment, even when a subject is low illumination and a light quantity monitor is unable to store prescribed charges within a maximum integration time in a CCD multiline sensor 100 as an image sensor which has plural optical sensors and a light quantity monitor receiving the light of the average light quantity of the optical sensors in a CCD sensor light monitoring part 101.

Comparators CP1 to CP3 of an integration state decision circuit 106 decide the level of an output 51 of a light quantity monitor at a maximum integration time arrival point of time, when a subject is at low illumination, switches SW1 to SW3 of a multiplication circuit 104 are turned on/off according to the decided results, and the gain of an operational amplifier OP1 amplifying a pixel signal 5 being an output of an optical sensor is subjected to variable setting. Here, circuits in a CCD multiline sensor 100 are provided on the same semiconductor chip, and time other than integration time is reduced to the utmost, without depending on an external controller 200 on the level decision of a monitor output and the gain setting of the multiplication circuit, as in the conventional practice.