A method for producing zinc alloy in which Si is contained in Zn, the method comprising: a process of heating metal Zn in a crucible provided in a heating furnace to melt the metal Zn so as to obtain Zn molten metal; a process of adding metal Si powder to the Zn molten metal in an amount capable of being melted at a temperature equal to or lower than a boiling point of Zn, and heating the resultant mixture to melt the metal Si powder in a state in which arising of the metal Si powder is suppressed by a floating suppressing member that is displaceable inside of the crucible, and a liquid surface of the Zn molten metal is coated with a carbonaceous material, the carbonaceous material being charcoal; wherein the floating supporting member includes an inner lid that is slidable along an inner circumferential surface of the crucible, and a rod that supports the inner lid and vertically moves the inner lid; wherein the inner lid is constituted by a mesh-like body having a mesh smaller than a diameter of the metal Si powder or wherein the inner lid has a plurality of through-holes having a diameter smaller than a diameter of the metal Si powder; a process of releasing the suppression of the floating of the metal Si powder by raising the inner lid of the floating suppressing member by the rod to allow the melted Si to be dispersed in the Zn molten metal so as to obtain Zn-Si alloy molten metal; and a process of filling a copper casting mold with the Zn-Si alloy molten metal, and rapidly cooling down the Zn-Si alloy molten metal by rapidly cooling down through water cooling an outer circumferential surface of the copper casting mold so as to obtain a billet; wherein the metal Si powder is added to the Zn molten metal in a range of 0.1% by mass to 4.0% by mass with respect to a total amount of the Zn-Si alloy to be obtained. a process of heating metal Zn in a crucible provided in a heating furnace to melt the metal Zn so as to obtain Zn molten metal; a process of adding metal Si powder to the Zn molten metal in an amount capable of being melted at a temperature equal to or lower than a boiling point of Zn, and heating the resultant mixture to melt the metal Si powder in a state in which arising of the metal Si powder is suppressed by a floating suppressing member that is displaceable inside of the crucible, and a liquid surface of the Zn molten metal is coated with a carbonaceous material, the carbonaceous material being charcoal; wherein the floating supporting member includes an inner lid that is slidable along an inner circumferential surface of the crucible, and a rod that supports the inner lid and vertically moves the inner lid; wherein the inner lid is constituted by a mesh-like body having a mesh smaller than a diameter of the metal Si powder or wherein the inner lid has a plurality of through-holes having a diameter smaller than a diameter of the metal Si powder; a process of releasing the suppression of the floating of the metal Si powder by raising the inner lid of the floating suppressing member by the rod to allow the melted Si to be dispersed in the Zn molten metal so as to obtain Zn-Si alloy molten metal; and a process of filling a copper casting mold with the Zn-Si alloy molten metal, and rapidly cooling down the Zn-Si alloy molten metal by rapidly cooling down through water cooling an outer circumferential surface of the copper casting mold so as to obtain a billet; wherein the metal Si powder is added to the Zn molten metal in a range of 0.1% by mass to 4.0% by mass with respect to a total amount of the Zn-Si alloy to be obtained.