Patent ID: 8194111

Claim:
A light-emitting element head, comprising: a plurality of light-emitting element chips in each of which a plurality of transfer elements and a plurality of light-emitting elements are arrayed in a line, the plurality of light-emitting elements being provided corresponding to the plurality of transfer elements; a lighting signal supply unit for supplying a plurality of lighting signals, each of the plurality of lighting signals corresponding to a respective one of N groups into which the plurality of light-emitting element chips are divided, and being provided to each of the light-emitting element chips that belong to the respective one of the N groups, where N is an integer of 2 or more; and a clock signal supply unit for supplying a first clock signal as a transfer signal for causing the plurality of light-emitting elements of each of the plurality of light-emitting element chips to sequentially emit light, the first clock signal being supplied to each of the plurality of light-emitting element chips in a common manner, and a plurality of second clock signals for setting the plurality of light-emitting elements ready to emit light, the plurality of second clock signals being supplied to respective light-emitting element chips belonging to a said group, and being supplied in a common manner across the N groups, wherein each of the plurality of second clock signals is provided with a plurality of periods falling within a period in which one of the plurality of transfer elements of each of the plurality of light-emitting element chips is kept turned on by the first clock signal, the number of the plurality of periods being determined according to the number of combinations of light emission and non-light emission of the plurality of light-emitting element chips included in each of the N groups, each of the combinations corresponding to a respective one of the plurality of periods, the clock signal supply unit supplies the plurality of second clock signals on the basis of the combinations, such that a transfer element adjacent to a turned-on transfer element in the direction of sequential lighting of the light-emitting elements is set to turn on, and the lighting signal supply unit starts supplying each of the plurality of lighting signals in a period that corresponds to a respective one of the combinations of the light emission and non-light emission of the light-emitting element chips in each of the N groups, among the plurality of periods provided for each of the plurality of second clock signals.