An inkjet printing machine comprising: an inkjet head; an ink an ink cartridge disposed at a position lower than that of the inkjet head and configured to hold the ink therein; an ink route configured to connect the ink cartridge to the inkjet head, the ink route including a direct route, a cartridge-side route connecting the ink cartridge to the direct route, and a head-side route connecting the direct route to the inkjet head; a branch route with one end connected to a branching point on the ink route at which the cartridge-side route and the direct route are connected to each other and the other end connected to a joining point on the ink route at which the direct route and the head-side route are connected to each other; a pump disposed on the branch route and used to send ink from the ink cartridge to the inkjet head; a valve disposed on the direct route which is a route between the branching point and the joining point and configured to open and close a channel for a fluid within the direct route; and controlling means configured to (i) close the valve and drive the pump in initial filling of the inkjet head with ink, (ii) let a tip of ink introduced into the ink route by drive of the pump reach a prescribed position on the head-side route higher than the ink cartridge, stop the pump and open the valve on or after a time point when the tip of ink reaches the prescribed position, (iii) allow the ink in the ink route to flow backward toward the ink cartridge by a water head difference between the ink cartridge and the tip of the ink in the head-side route with the valve opened to move the air in the direct route into the ink cartridge and close the valve after the air in the direct route is moved into the ink cartridge, and (iv) drive the pump to fill the inkjet head with ink. an inkjet head; an ink an ink cartridge disposed at a position lower than that of the inkjet head and configured to hold the ink therein; an ink route configured to connect the ink cartridge to the inkjet head, the ink route including a direct route, a cartridge-side route connecting the ink cartridge to the direct route, and a head-side route connecting the direct route to the inkjet head; a branch route with one end connected to a branching point on the ink route at which the cartridge-side route and the direct route are connected to each other and the other end connected to a joining point on the ink route at which the direct route and the head-side route are connected to each other; a pump disposed on the branch route and used to send ink from the ink cartridge to the inkjet head; a valve disposed on the direct route which is a route between the branching point and the joining point and configured to open and close a channel for a fluid within the direct route; and controlling means configured to (i) close the valve and drive the pump in initial filling of the inkjet head with ink, (ii) let a tip of ink introduced into the ink route by drive of the pump reach a prescribed position on the head-side route higher than the ink cartridge, stop the pump and open the valve on or after a time point when the tip of ink reaches the prescribed position, (iii) allow the ink in the ink route to flow backward toward the ink cartridge by a water head difference between the ink cartridge and the tip of the ink in the head-side route with the valve opened to move the air in the direct route into the ink cartridge and close the valve after the air in the direct route is moved into the ink cartridge, and (iv) drive the pump to fill the inkjet head with ink. (i) close the valve and drive the pump in initial filling of the inkjet head with ink, (ii) let a tip of ink introduced into the ink route by drive of the pump reach a prescribed position on the head-side route higher than the ink cartridge, stop the pump and open the valve on or after a time point when the tip of ink reaches the prescribed position, (iii) allow the ink in the ink route to flow backward toward the ink cartridge by a water head difference between the ink cartridge and the tip of the ink in the head-side route with the valve opened to move the air in the direct route into the ink cartridge and close the valve after the air in the direct route is moved into the ink cartridge, and (iv) drive the pump to fill the inkjet head with ink.