PURPOSE: To facilitate the inspection of pin electrodes with a small load factor by arranging a means of gemerating square wave signals selectively or cyclicly and a means of fixedly generating an output or interrupting it from arbitrary signals so as to provide specified actions thereof.

CONSTITUTION: Outputs of output terminals 19-1, 19-2... are written sequentially into four registers of electrostatic printers each time a data strobe signal is generated. After the writing into the four registers, outputs of each registor are provided in parallel to corresponding electrode drivers. When outputs of the output terminals 19-1, 19-2... are at a low level, a printing surface is charged at a part contacting corresponding pin electrodes via the electrode drives and indicates dots by development thereof. The pin electrodes are arranged sequentially by four groups and outputs of each electrode driver are switched by print end signal to be connected to corresponding pin electrodes of each group. When the application of voltage to the pin electrodes of all the groups is finished, printing for one line is completed.