PURPOSE: To realize automatic switching for converting a data which has been inputted in parallel, to serial, and outputting as it is a data which has been inputted in serial, by a simple constitution, by providing a serial-parallel converting means for reading successively a data from a storage means in response to the first or the second selected clock, converting this data to serial and outputting it.

CONSTITUTION: An input data which has been transferred from an input data receiving art 10 is stored alternately at every one scanning line in a pair of line memories 22, 24 through an SW11 and an SW12 provided on its input side. The stored data of a one scanning line portion is read out alternately at every one scanning line from the line memories 22, 24 through switches SW21, SW22. A serial-parallel converter 30 reads out successively an input data from a storage part 20, and when the input data is a parallel data, it is converted to a serial data. The converted series data DS is outputted to a laser printer from a terminal 200, in case of this embodiment.