A manufacturing method of a galvannealed steel sheet, the manufacturing method comprising: circulating a coating bath which is a molten metal including a molten zinc and a molten aluminum in order of a coating tub, a separating tub, and an adjusting tub; coating a steel sheet which is dipped in the coating bath at the coating tub in which the coating bath transferred from the adjusting tub is stored at a predetermined bath temperature T1; separating by a flotation a top-dross which is precipitated by controlling an aluminum concentration A2 of the coating bath transferred from the coating tub to be 0.14 mass% or more at the separating tub in which the coating bath transferred from the coating tub to the separating tub is stored at a bath temperature T2 which is lower than the bath temperature T1 of the coating tub and a first zinc-included-metal which includes an aluminum with a concentration higher than an aluminum concentration A1 of the coating bath in the coating tub is supplied; and adjusting an aluminum concentration A3 of the coating bath transferred from the separating tub to a concentration which is higher than the aluminum concentration A1 and is lower than the aluminum concentration A2 at the adjusting tub in which the coating bath transferred from the separating tub is stored at a bath temperature T3 which is higher than the bath temperature T2 of the separating tub and a second zinc-included-metal which includes an aluminum with a concentration lower than the aluminum concentration A2 of the coating bath in the separating tub or does not include an aluminum is supplied, wherein the bath temperature T2 of the separating tub is controlled to be lower 5°C or more as compared with the bath temperature T1 of the coating tub and to be higher than a melting point of the molten metal, wherein the bath temperature T3 is controlled so that the bath temperature T1, the bath temperature T2, and the bath temperature T3 satisfy the following formula and the following formula in celsius degree, when a difference of a bath temperature decrease of the coating bath when transferred from the adjusting tub to the coating tub is ΔT fall in celsius degree: T 1 + ΔT fall − 10 ≤ T 3 ≤ T 1 + ΔT fall + 10 T 2 + 5 ≤ T 3 wherein a circulating volume of the coating bath per one hour satisfies one or both of the following conditions: (i) a storage of the coating bath in the coating tub is five times or less of the circulating volume of the coating bath per one hour; (ii) a storage of the coating bath in the separating tub is two times or more of the circulating volume of the coating bath per one hour, and wherein the aluminum concentration A1 of the coating bath in the coating tub is 0.125 mass% to 0.14 mass%. circulating a coating bath which is a molten metal including a molten zinc and a molten aluminum in order of a coating tub, a separating tub, and an adjusting tub; coating a steel sheet which is dipped in the coating bath at the coating tub in which the coating bath transferred from the adjusting tub is stored at a predetermined bath temperature T1; separating by a flotation a top-dross which is precipitated by controlling an aluminum concentration A2 of the coating bath transferred from the coating tub to be 0.14 mass% or more at the separating tub in which the coating bath transferred from the coating tub to the separating tub is stored at a bath temperature T2 which is lower than the bath temperature T1 of the coating tub and a first zinc-included-metal which includes an aluminum with a concentration higher than an aluminum concentration A1 of the coating bath in the coating tub is supplied; and adjusting an aluminum concentration A3 of the coating bath transferred from the separating tub to a concentration which is higher than the aluminum concentration A1 and is lower than the aluminum concentration A2 at the adjusting tub in which the coating bath transferred from the separating tub is stored at a bath temperature T3 which is higher than the bath temperature T2 of the separating tub and a second zinc-included-metal which includes an aluminum with a concentration lower than the aluminum concentration A2 of the coating bath in the separating tub or does not include an aluminum is supplied, (i) a storage of the coating bath in the coating tub is five times or less of the circulating volume of the coating bath per one hour; (ii) a storage of the coating bath in the separating tub is two times or more of the circulating volume of the coating bath per one hour, and