A threshold matrix generation method of generating a threshold matrix which is compared with a grayscale original image in halftoning said original image, comprising: a) a step (S11 to S15) of acquiring an element matrix representing an arrangement of dots in a gray level of 50 % in a matrix area where a threshold matrix is generated; and b) a step of determining a threshold value of each element in said matrix area, and characterized in that a plurality of types of basic tiles (731 to 736) each of which is an arrangement of elements in two rows and two columns consisting of two ON elements each representing existence of a dot and two OFF elements each representing absence of a dot are prepared, and a plurality of basic tiles each of which is one of said plurality of types of basic tiles are arranged in said matrix area in accordance with a prohibition condition for at least prohibiting an arrangement of only ON elements or OFF elements in an area of two rows and two columns, to acquire said element matrix in said step a), and said step a) comprises: a1) a step (S 13) of setting a basic tile of one type at arbitrary one tile position in said matrix area; a2) a step of setting a new basic tile of said one type at a tile position which is farthest from basic tiles of said one type in accordance with said prohibition condition, on the premise of spatial repetition of said threshold matrix; and a3) a step of repeating said step a2) by a predetermined number of times, said threshold matrix generation method further comprises, between said steps a) and b): c) a step of setting a dot at arbitrary one element on a highlight dot pattern which is a set of ON elements in said element matrix; d) a step (S17, S18) of repeating a process of adding a new dot to an element on said highlight dot pattern, said new dot being farthest from existing dots on said highlight dot pattern, on the premise of spatial repetition of said threshold matrix in halftoning of an original image, or repeating said process in accordance with a predetermined condition, to determine a turn-on order in which dots are added to elements in accordance with increase in gray level on a highlight side; e) a step (S 19) of setting dots at all elements excluding arbitrary one element on a shadow dot pattern which is a set of OFF elements in said element matrix; and f) a step (S20, S21) of repeating a process of removing a dot of an element on said shadow dot pattern, said dot being farthest from elements in each of which a dot is not set on said shadow dot pattern, on the premise of spatial repetition of said threshold matrix, to determine a turn-off order in which dots are removed from elements in accordance with decrease in gray level on a shadow side, and said threshold value of said each element in said matrix area is determined in accordance with said turn-on order and said turn-off order in said step b). a) a step (S11 to S15) of acquiring an element matrix representing an arrangement of dots in a gray level of 50 % in a matrix area where a threshold matrix is generated; and b) a step of determining a threshold value of each element in said matrix area, and characterized in that a1) a step (S 13) of setting a basic tile of one type at arbitrary one tile position in said matrix area; a2) a step of setting a new basic tile of said one type at a tile position which is farthest from basic tiles of said one type in accordance with said prohibition condition, on the premise of spatial repetition of said threshold matrix; and a3) a step of repeating said step a2) by a predetermined number of times, c) a step of setting a dot at arbitrary one element on a highlight dot pattern which is a set of ON elements in said element matrix; d) a step (S17, S18) of repeating a process of adding a new dot to an element on said highlight dot pattern, said new dot being farthest from existing dots on said highlight dot pattern, on the premise of spatial repetition of said threshold matrix in halftoning of an original image, or repeating said process in accordance with a predetermined condition, to determine a turn-on order in which dots are added to elements in accordance with increase in gray level on a highlight side; e) a step (S 19) of setting dots at all elements excluding arbitrary one element on a shadow dot pattern which is a set of OFF elements in said element matrix; and f) a step (S20, S21) of repeating a process of removing a dot of an element on said shadow dot pattern, said dot being farthest from elements in each of which a dot is not set on said shadow dot pattern, on the premise of spatial repetition of said threshold matrix, to determine a turn-off order in which dots are removed from elements in accordance with decrease in gray level on a shadow side, and