An ink supply device for a printhead includes an ink cartridge and a damper device. The ink cartridge is connected to the printhead through a flexible tube. The printhead is mounted on a carriage that reciprocates, and discharges an ink drop to perform printing. The damper device is mounted on the carriage to relax pressure fluctuation of ink supplied from the ink cartridge to the printhead. The damper device has a case, an ink introduction passage, and a flexible plate. The case defines a pressure chamber communicated with the printhead. The ink introduction passage is communicated with the flexible tube, and is ated with the pressure chamber. The flexible plate is provided so as to define a part of the pressure chamber, and has a waveform portion formed with a plurality of waveforms.