A liquid supply device includes a liquid discharge head, a main tank, a first sub-tank, a second sub-tank, a first channel, a degassing device, and a second channel. The liquid discharge head is configured to discharge liquid. The main tank is configured to store liquid to be supplied to the liquid discharge head. The first sub-tank is configured to store gas and liquid and connected to the main tank and the liquid discharge head. The second sub-tank is configured to store gas and liquid and connected to the first sub-tank and the liquid discharge head. The first channel connects between the main tank and the first sub-tank. The degassing device is configured to degas liquid in the first channel. The second channel connects between the second sub-tank and the first channel.