An inkjet printer has a backflow prevention valve disposed to bottom of subtanks to of the diaphragm pump unit mounted on a carriage, and causes ink passing through the backflow prevention valve to flow to the inkjet head side. A support orifice that supports an umbrella-shaped valve plug, a port formed at a position circumferentially eccentric to the center of the support orifice, and a fluid conduction channel extending from an edge of the port circumferentially around the support orifice are disposed to the valve plug seating surface of the backflow prevention valve. A discharge orifice that discharges ink to the inkjet head side is disposed in the outside wall of the valve plug seating surface, and the discharge orifice and port are formed on the same side of the center of the support orifice.