A tin mill black plate manufacturing method for obtaining a tin mill black plate comprising, on a surface of a steel sheet, a chromium metal layer and a hydrated chromium oxide layer stacked in this order from a steel sheet side, wherein the chromium metal layer has a coating weight of 50 to 160 mg/m 2, wherein the hydrated chromium oxide layer has a coating weight of more than 15 mg/m 2 but not more than 30 mg/m 2 in terms of chromium amount, and wherein the chromium metal layer includes a base portion with a thickness of not less than 7.0 nm and granular protrusions provided on the base portion and having a maximum diameter of not more than 150 nm and a number density per unit area of not less than 1 000 protrusions/μm 2, by use of an aqueous solution containing a hexavalent chromium compound, a fluorine-containing compound and sulfuric acid, the method comprising: the step of subjecting a steel sheet to treatment 1 including cathodic electrolysis treatment C1 using the aqueous solution; the step of subjecting the steel sheet having undergone the cathodic electrolysis treatment C1 to treatment 2 including anodic electrolysis treatment A1 and cathodic electrolysis treatment C2 following the anodic electrolysis treatment A1, using the aqueous solution, at least two times; and the step of subjecting the steel sheet having undergone the treatment 2 at least two times to cathodic electrolysis treatment as post-treatment using an aqueous solution containing a hexavalent chromium compound; wherein the maximum diameter and number density per unit area of the granular protrusions are obtained by: subjecting a surface of the tin mill black plate having formed thereon the chromium metal layer and the hydrated chromium oxide layer to carbon deposition to produce an observation sample by an extraction replica method; taking a micrograph of the sample at a magnification of 20 000X with a scanning transmission electron microscope, binarizing the micrograph using software and subjecting the micrograph to image analysis; and determining the diameter, as a true circle-equivalent value, and the number density per unit area through back calculation from the area occupied by the granular protrusions, the maximum diameter being the diameter that is maximum in observation fields as obtained by taking micrographs of five fields at a magnification of 20 000X, and the number density per unit area being the average of number densities of the five fields. wherein the chromium metal layer has a coating weight of 50 to 160 mg/m 2, wherein the hydrated chromium oxide layer has a coating weight of more than 15 mg/m 2 but not more than 30 mg/m 2 in terms of chromium amount, and wherein the chromium metal layer includes a base portion with a thickness of not less than 7.0 nm and granular protrusions provided on the base portion and having a maximum diameter of not more than 150 nm and a number density per unit area of not less than 1 000 protrusions/μm 2, by use of an aqueous solution containing a hexavalent chromium compound, a fluorine-containing compound and sulfuric acid, the method comprising: the step of subjecting a steel sheet to treatment 1 including cathodic electrolysis treatment C1 using the aqueous solution; the step of subjecting the steel sheet having undergone the cathodic electrolysis treatment C1 to treatment 2 including anodic electrolysis treatment A1 and cathodic electrolysis treatment C2 following the anodic electrolysis treatment A1, using the aqueous solution, at least two times; and the step of subjecting the steel sheet having undergone the treatment 2 at least two times to cathodic electrolysis treatment as post-treatment using an aqueous solution containing a hexavalent chromium compound; wherein the maximum diameter and number density per unit area of the granular protrusions are obtained by: subjecting a surface of the tin mill black plate having formed thereon the chromium metal layer and the hydrated chromium oxide layer to carbon deposition to produce an observation sample by an extraction replica method; taking a micrograph of the sample at a magnification of 20 000X with a scanning transmission electron microscope, binarizing the micrograph using software and subjecting the micrograph to image analysis; and determining the diameter, as a true circle-equivalent value, and the number density per unit area through back calculation from the area occupied by the granular protrusions, the maximum diameter being the diameter that is maximum in observation fields as obtained by taking micrographs of five fields at a magnification of 20 000X, and the number density per unit area being the average of number densities of the five fields.