providing a printing head having a plurality of nozzles arranged in a row in an arrangement direction, wherein the distance between any two neighboring nozzles is P;

determining an angle θ that makes (P×cos θ)/YO and (P×sin θ)/XO both be closest to positive integers by calculating (P×cos θ)/YO and (P×sin θ)/XO at every an interval of a predetermined angle from an initial angle of θ, wherein the distance between the dots of a data to be printed in the first direction is X0, and the distance between the dots of the data to be printed in the second direction perpendicular to the first direction is Y0;

increasing the resolution of the data to be printed, such that a distance between the dots of the data to be printed with increased resolution in the first direction is X1, and a distance between the dots of the data to be printed with increased resolution in the second direction is Y1;

rotating the printing head, such that an angle exists between the arrangement direction and the second direction is the determined angle θ, P×sin θ is substantially an integral multiples of X1, and P×cos θ is substantially an integral multiples of Y1; and

printing with the rotated printing head.