A kit of parts includes a tubing component having at least two in-line sections with different external diameters and a set of connection devices. and of which controllability of charged potential of a photoreceptor is hardly impaired even with a some amount of contaminants such as a toner so that control of charged potential of a photoreceptor can be stably carried out to fall in an appropriate range over a long period of time, and moreover which is inexpensive. When the delay time has passed, reading data out from the buffer starts.