A halftone mask manufacturing method of manufacturing a halftone mask to be applied to a halftone process of creating a halftone image by converting multivalued image data, the method comprising: a dot pattern determining step of determining a dot pattern at a dot pattern determining target gradation, which is a gradation having a gradation difference of one or more gradations from a dot pattern determined gradation as a gradation at which a dot pattern indicating whether or not there is a dot is already determined and is a gradation of a target for determining a dot pattern based on the dot pattern at the dot pattern determined gradation, consecutively changing the dot pattern determining target gradation, and determining dot patterns for a plurality of gradations, wherein the dot pattern determining step is characterized by a dot number changing step of determining a temporary dot pattern at the dot pattern determining target gradation by removing or adding dots as much as the number of dots corresponding to the gradation difference between the dot pattern determined gradation and the dot pattern determining target gradation from or to the dot pattern at the dot pattern determined gradation, a graininess evaluation step, and a replacement processing step of determining the dot pattern at the dot pattern determining target gradation by performing a replacement process of replacing dots including some of the dots at the dot pattern determined gradation with non-dot arrangements on the temporary dot pattern, or a replacement processing step of determining a temporary dot pattern at the dot pattern determined gradation by performing a replacement process of replacing some of dots with non-dot arrangements on the dot pattern at the dot pattern determined gradation, a graininess evaluation step, and a dot number changing step of determining the dot pattern at the dot pattern determining target gradation by removing or adding the dots as much as the number of dots corresponding the gradation difference between the dot pattern determined gradation and the dot pattern determining target gradation from or to the temporary dot pattern. a dot pattern determining step of determining a dot pattern at a dot pattern determining target gradation, which is a gradation having a gradation difference of one or more gradations from a dot pattern determined gradation as a gradation at which a dot pattern indicating whether or not there is a dot is already determined and is a gradation of a target for determining a dot pattern based on the dot pattern at the dot pattern determined gradation, consecutively changing the dot pattern determining target gradation, and determining dot patterns for a plurality of gradations, wherein the dot pattern determining step is characterized by a dot number changing step of determining a temporary dot pattern at the dot pattern determining target gradation by removing or adding dots as much as the number of dots corresponding to the gradation difference between the dot pattern determined gradation and the dot pattern determining target gradation from or to the dot pattern at the dot pattern determined gradation, a graininess evaluation step, and a replacement processing step of determining the dot pattern at the dot pattern determining target gradation by performing a replacement process of replacing dots including some of the dots at the dot pattern determined gradation with non-dot arrangements on the temporary dot pattern, or a replacement processing step of determining a temporary dot pattern at the dot pattern determined gradation by performing a replacement process of replacing some of dots with non-dot arrangements on the dot pattern at the dot pattern determined gradation, a graininess evaluation step, and a dot number changing step of determining the dot pattern at the dot pattern determining target gradation by removing or adding the dots as much as the number of dots corresponding the gradation difference between the dot pattern determined gradation and the dot pattern determining target gradation from or to the temporary dot pattern.