An inkjet printer comprising: an image-forming part that forms an auxiliary layer on a base material by ejecting droplets of an auxiliary ink toward said base material and forms an image on said auxiliary layer by ejecting droplets of an image-forming ink toward said base material, said auxiliary ink changing a dot formation state of droplets of said image-forming ink; and characterized in that said inkjet printer further comprises: a storage part that stores a reference table that associates each of a plurality of types of base materials with a proper dot area rate to be used when forming said auxiliary layer, said proper dot area rate being a minimum dot area rate for forming the auxiliary layer where droplets of said image-forming ink are fixed to form dots of a certain size on a surface of said base material, and where droplets of the image-forming ink applied neither overspread not overpenetrate, said dot area rate being a proportion of the number of positions in which droplets of said auxiliary ink are actually applied in an area of predetermined size on said base material with respect to the total number of positions in which droplets of said auxiliary ink can be applied; and a dot-area-rate determination part that determines a dot area rate to be used when forming said auxiliary layer on a target base material on which an image is to be formed, as an auxiliary ink dot area rate, by referencing said reference table using a type of said target base material, wherein said image-forming part forms said auxiliary layer in accordance with said auxiliary ink dot area rate. an image-forming part that forms an auxiliary layer on a base material by ejecting droplets of an auxiliary ink toward said base material and forms an image on said auxiliary layer by ejecting droplets of an image-forming ink toward said base material, said auxiliary ink changing a dot formation state of droplets of said image-forming ink; and characterized in that said inkjet printer further comprises: a storage part that stores a reference table that associates each of a plurality of types of base materials with a proper dot area rate to be used when forming said auxiliary layer, said proper dot area rate being a minimum dot area rate for forming the auxiliary layer where droplets of said image-forming ink are fixed to form dots of a certain size on a surface of said base material, and where droplets of the image-forming ink applied neither overspread not overpenetrate, said dot area rate being a proportion of the number of positions in which droplets of said auxiliary ink are actually applied in an area of predetermined size on said base material with respect to the total number of positions in which droplets of said auxiliary ink can be applied; and a dot-area-rate determination part that determines a dot area rate to be used when forming said auxiliary layer on a target base material on which an image is to be formed, as an auxiliary ink dot area rate, by referencing said reference table using a type of said target base material, wherein a storage part that stores a reference table that associates each of a plurality of types of base materials with a proper dot area rate to be used when forming said auxiliary layer, said proper dot area rate being a minimum dot area rate for forming the auxiliary layer where droplets of said image-forming ink are fixed to form dots of a certain size on a surface of said base material, and where droplets of the image-forming ink applied neither overspread not overpenetrate, said dot area rate being a proportion of the number of positions in which droplets of said auxiliary ink are actually applied in an area of predetermined size on said base material with respect to the total number of positions in which droplets of said auxiliary ink can be applied; and a dot-area-rate determination part that determines a dot area rate to be used when forming said auxiliary layer on a target base material on which an image is to be formed, as an auxiliary ink dot area rate, by referencing said reference table using a type of said target base material, wherein said image-forming part forms said auxiliary layer in accordance with said auxiliary ink dot area rate.