PURPOSE: To effect charging of an ink mist efficiently, and to restrain the ink mist invading a corona generator provided on the way of an ink flow route, by feeding air to pass it in the direction of ink circulation in flow route of the ink.

CONSTITUTION: Corona generator 51 having the opening 48 directed to the first flow route 44 of ink is provided on its way. Through hole 54 for air supply is formed through part of metallic cylinder 53 of generator 51, air is supplied through flexible tube 55, such as a rubber hose. Hole 54 is formed through a part of cylinder 53 opposite to the backside of generator 51, that is, opening 48, the air supplied passes through the inside of generator 51, and then flows through opening 48 to route 44, thus permitting charging of the ink mist to be efficiently effected, and invasion of the mist into the corona generator to be restrained.