In an inkjet printer, when an amount of ink in a supply side sub tank is an appropriate amount and an amount of ink in the discharge side sub tank is an appropriate amount, the ink is supplied from the discharge side sub tank to the supply side sub tank at a constant flow rate by an ink pump. Furthermore, the inkjet printer acquires a first pump driving speed, which is the driving speed of the ink pump at this time, at a predetermined time interval, and compares the first pump driving speed with a predetermined reference speed, and executes a predetermined error processing when the first pump driving speed exceeds a reference speed.