PURPOSE: To prevent uneven density on a printing surface eliminating partial unevenness of a water film on a chrome roller surface by alternately introducing a compressed air to or discharging it from right and left partition chambers divided at the center in a hollow of a chrome roller.

CONSTITUTION: A rotary partition plate 14 is provided at the middle part of a roller support shaft 9 of a chrome roller 4 to form right and left partition chambers 18 and 18' by air sealing with seal members 16 and 17. A compressed air is alternately introduced into right and left partition chambers 18 and 18' via introduction holes 20 and 20' in a roller support shaft 9 through pipes 19 and 19' from an compressed air source. The oscillation range is regulated by oscillation range regulating discs 21 and 21'.