A steel plate for use in a fuel tank and equipped with a Zn-Ni alloy plating layer positioned on one or both surfaces of a ferrite, and a chromate-free conversion coating positioned on top of the Zn-Ni alloy plating layer, wherein the Zn-Ni alloy plating layer has cracks extending from the interface with the chromate-free conversion coating to the interface with the steel plate, and the chromate-free conversion coating comprises: an organic silicon compound comprising the polycondensate of a silane coupling agent; a phosphate compound and/or a phosphonic acid compound; a vanadium compound; and a titanium compound and/or a zirconium compound. Furthermore, the total concentration per surface of the phosphate compound and/or phosphonic acid compound + the vanadium compound + the titanium compound and/or zirconium compound constitutes 5-20 mass% or less, when calculated in terms of the metal content thereof.