An inkjet image forming apparatus includes print heads, a first tank, an ink circulation line, and a controller. The ink circulation line includes an ink supply line for supplying ink from the first tank to the print heads, and an ink return line for returning ink collected from the print heads to a second tank. The controller controls line elements of the ink circulation line, to adjust a magnitude relation between a first product and a second product, in accordance with the type of ink. The first product is a product of factors including a flow passage length along, a viscosity of ink in, and a fluid resistance coefficient of the ink supply line. The second product is a product of factors including a flow passage length along, a viscosity of ink in, and a fluid resistance coefficient of the ink return line.