There is provided a technique in which a retracting operation of a bundle of sheets from a stapler after a staple process can be stably performed irrespective of the number of sheets constituting the bundle of sheets or the transport resistance. To prevent the peak splitting, it is necessary to raise efficiency of adenylation a single peak to occur without changing reaction conditions. The processes involve treating the substrate to reduce the concentration of chemical species on the surface of or in the substrate without altering the bulk physical properties of the device or article, and thereafter forming a grafted polymer layer on the treated substrate surface. The bias voltage circuit initially accelerates the charging of the transistor gates, and subsequently completes charging the gates at a slower rate.