The invention discloses an ink supplying device of a rotary type letterpress printing machine. The ink supplying device comprises a box body, an outlet and a sealing device, wherein the box body is used for containing ink; the outlet is mounted at the bottom of the box body; and the sealing device is mounted on the box body. By means of the ink supplying device of the rotary type letterpress printing machine, it is guaranteed that the ink in the printing state is in the smooth state, and therefore smoothness of the ink in the printing state can be improved. A balancing device is arranged on an upper cover plate, so that the air pressures inside and outside the ink supplying device of the rotary type letterpress printing machine are balanced all the time, and thus the situation that the ink leaks due to excessively-high gas pressure generated in the printing state is avoided.