Abstract: A photoconductive device having a photoconductive layer which includes an amorphous semiconductor layer capable of charge multiplication in at least a part thereof is disclosed. The method of operating such a photoconductive device is also disclosed. By using the avalanche effect of the amorphous semiconductor layer, it is possible to realize a highly sensitive photoconductive device while maintaining low lag property. In one aspect of the present invention, the amorphous semiconductor layer is amorphous Se. In another aspect of the present invention, the amorphous semiconductor layer is composed mainly of tetrahedral elements including at least an element of hydrogen or halogens. When using the amorphous semiconductor layer composed mainly of tetrahedral elements, the charge multiplication effect is produced mainly in the interior of the amorphous semiconductor, and thus it is possible to obtain a thermally stable photoconductive device having a high sensitivity while keeping a good photoresponse.