The invention provides an ink supply device. The ink supply device is used for supplying ink to a printer. The ink supply device comprises ink bags, volume measurement bags and a signal device. One end of each volume measurement bag is connected with the corresponding ink bag through a pipe, and the other end of each volume measurement bag is connected with the printer through a pipe. The signal device is used for detecting volume changes of the volume measurement bags. The signal device is electrically connected with a controller of the printer. When the volume change of each volume measurement bag is greater than a preset value, the signal device transmits signals to the controller. The controller stops printing operation of the printer. According to the ink supply device, the ink bags and the volume measurement bags are all arranged outside ink cartridges, and ink replacing and ink charging are easy; the volume measurement bag are small-volume bags; even if the ink cartridges need to be replace, only the volume measurement bags need to be replaced, and loss is little; furthermore, the ink supply device senses the ink shortage conditions better through early warning of the signal device to remind users of timely replacement of ink bags; meanwhile, transparent side plates are arranged around an ink bag suspension device so that the users can observe the volume changes of ink in the ink bags only with eyes and replace the ink bags in time.