PURPOSE: To contrive the improvement in S/N ratio of the output by a method wherein the degree of effects of the FET capacitance on the total output capacitance is reduced by decreasing the number of video transmission FETs connected at once to the output terminal of a sensor.

CONSTITUTION: FETs are arranged in multi arrays: the first array is composed of 3 pieces × 4 groups, and each of its drains is connected in common to the output terminal 16; the second array 4 pieces × 12 groups, and the drain to each of the sources of the first array; the third array 4 pieces × 48 groups, and the drain to the sources of the second array; the fourth array 4 pieces × 192 groups, and the drain to the sources of the third array; finally, the sources are connected to each output of a sensor array 10. In the case of the output number N of the array 10, the number of elements of each group of the K-th array is selected as nK≥N. Only one element is conducted at once in every array by selectively driving the gates of FETs in each array in connection to an additional circuit 20 by means of a horizontal register 18, with the result that each output terminal 16 is conducted via only one branch path. Thus, all the drain capacitances markedly reduce by a factor of some increase or more in wiring capacitance. Accordingly, the S/N ratio of output is largely improved.