A method for adjusting a head module of an inkjet head in which a plurality of head modules having nozzles capable of ejecting droplets are connected and linked together is disclosed. The inkjet head has an overlapping region in which an arrangement sequence of the head modules corresponding to the ejected droplets is alternate between adjacent head modules. The method includes the steps of: obtaining, among intervals between the droplet ejected by one of the head modules and the droplet ejected by another one of the head modules in the overlapping region, a largest interval between the droplets in a direction of alignment of the head modules based upon movement of the droplets caused by a landing interference; and adjusting the adjacent head modules in a direction to decrease the largest interval between the droplets.