A dot data generating method uses a first inkjet recording device and a second inkjet recording device, in which a first image is printed using the first inkjet recording device based on first dot data which determines formation or non-formation of dots, and second dot data is generated to print a second image based on the second dot data using the second inkjet recording device in which a speed of a relative movement of the inkjet head and a recording medium when printing an image is small compared to the first inkjet recording device. The dot data generating method includes generating the second dot data by converting the first dot data such that data of each dot in which formation of a dot is determined is converted to form a plurality of dots at predetermined intervals between the dots in a relative movement direction in place of the each dot.