A threshold matrix generating method of generating a threshold matrix which is compared with a grayscale original image in halftoning said original image, comprising: a) a step (S22 to S26) of determining a turn-on order in which halftone dots are added to elements in accordance with increase in gray level or a turn-off order in which halftone dots are removed from elements in accordance with decrease in gray level, in a matrix area where a threshold matrix is generated and a plurality of elements are arranged in a row direction and a column direction; and b) a step of determining a threshold value of each element in said matrix area in accordance with said turn-on order or said turn-off order, and characterized in that said threshold matrix generating method further comprises, before said step a), c) a step of sequentially assigning a plurality of linear areas (831 to 833), which are arranged in an arrangement direction without spaces in said matrix area, to a plurality of element groups (841 to 843) along said arrangement direction, each of said plurality of linear areas extending in a tilt direction tilted relatively to said row direction and said column direction, said arrangement direction being perpendicular to said tilt direction, said plurality of element groups respectively corresponding to a plurality of grayscale ranges acquired by dividing a whole grayscale range, centers of elements of each element group being included in linear areas assigned to said each element group, and arbitrary one element in each element group is specified to change said one element to a specified element and subsequently a process of changing another element in said each element group to a specified element is repeated, said another element being farthest from specified elements in said each element group, on the premise of spatial repetition of said threshold matrix in halftoning of an original image, or said process is repeated in accordance with a predetermined condition, to determine a turn-on order in which halftone dots are added to elements in said each element group in accordance with increase in gray level in a grayscale range corresponding to said each element group or a turn-off order in which halftone dots are removed from elements in said each element group in accordance with decrease in gray level in said grayscale range in said step a), and said threshold value of said each element is determined in accordance with a turn-on order (s) and/or a turn-off order (s) for said plurality of element groups in said step b). a) a step (S22 to S26) of determining a turn-on order in which halftone dots are added to elements in accordance with increase in gray level or a turn-off order in which halftone dots are removed from elements in accordance with decrease in gray level, in a matrix area where a threshold matrix is generated and a plurality of elements are arranged in a row direction and a column direction; and b) a step of determining a threshold value of each element in said matrix area in accordance with said turn-on order or said turn-off order, and characterized in that said threshold matrix generating method further comprises, before said step a), c) a step of sequentially assigning a plurality of linear areas (831 to 833), which are arranged in an arrangement direction without spaces in said matrix area, to a plurality of element groups (841 to 843) along said arrangement direction, each of said plurality of linear areas extending in a tilt direction tilted relatively to said row direction and said column direction, said arrangement direction being perpendicular to said tilt direction, said plurality of element groups respectively corresponding to a plurality of grayscale ranges acquired by dividing a whole grayscale range, centers of elements of each element group being included in linear areas assigned to said each element group, and arbitrary one element in each element group is specified to change said one element to a specified element and subsequently a process of changing another element in said each element group to a specified element is repeated, said another element being farthest from specified elements in said each element group, on the premise of spatial repetition of said threshold matrix in halftoning of an original image, or said process is repeated in accordance with a predetermined condition, to determine a turn-on order in which halftone dots are added to elements in said each element group in accordance with increase in gray level in a grayscale range corresponding to said each element group or a turn-off order in which halftone dots are removed from elements in said each element group in accordance with decrease in gray level in said grayscale range in said step a), and said threshold value of said each element is determined in accordance with a turn-on order (s) and/or a turn-off order (s) for said plurality of element groups in said step b).