A valve seat and a valve assembly incorporating such valve seat form tight dual seals with glass lined nozzle of a reagent or reaction vessel. At the front end of the grip, a rotary operating member to be used for prime mover rotation speed adjustment is rotatably mounted. The pills are dispensed from the bowl onto a sloped slide and counted at the bottom of the slide by an optical counter. The controller performs a charging voltage correcting operation in which the controller provides a test charging voltage to the charging unit for forming the developer image, and then a normal charging voltage for normal printing is determined based on the density. The pads may take on different shapes such as rectangular, oval or triangular shape to be able to be placed at different locations on the patient.