11b against the urging force of the return spring 11a as a result the ball 11c comes into abutment against the lower face of the base 6 of the oblique assembly to bring the oblique assembly 4 5 and 6 upward while in rolling contact to the position in which the upper face of the base 6 abuts against the stoppers 21 as indicated by the double dotted lines in fig2 by this upward push the leading edge of the blade 4 comes close to the circumference of the ink fountain roller 1 to form a container acting as the ink groove between the oblique assembly 4 5 and 6 and the circumference of the ink fountain roller 1 since the change over valve 14 is given the function of a check valve as shown in fig1 the oil pressure supplied to the hydraulic cylinder 11 is held at a proper level so that the oblique assembly 4 5 and 6 is stably held in the desired position in this close position the printing ink is supplied to the plate cylinder as the ink fountain roller 1 rotates in case the ink groove 3 is to be cleaned or maintained the change over valve 14 is switched to the side opposed to that shown in fig1 then the oil pressure is relieved and the rod 11b is retracted by the urging force of the return spring 11a in accordance with this the oil in the cylinder 11 is returned as the rod 11b is retracted the oblique assembly 4 5 and 6 is angularly displaced around the pins 2 and 2 to the position as indicated.