An image forming apparatus includes a head tank, a main tank, a pump, and a first control unit, so that when pressure in the head tank is not restored to a predetermined pressure while liquid is supplied from the main tank to the head tank, it is determined that the state of the main tank is an empty state, causing a pump to reversely supply a predetermined amount of liquid from the head tank to the main tank, and stopping printing; and further includes a second control unit, so that when emergency printing is instructed, opening the head tank to air, supplying liquid to the head tank, closing the head tank from air, and supplying liquid from the head tank to the main tank to generate a negative pressure in the head tank are performed.