A method for manufacturing a wet master batch, including preparing a carbon black slurry by dispersing carbon black in water, mixing a rubber latex and the carbon black slurry to cause a coagulation reaction to occur therein, to obtain a coagulation slurry, and subjecting the coagulation slurry to solid-liquid separation and dehydration, wherein the solid-liquid separation and dehydration comprises: filtering the coagulation slurry through a filter by gravity and depressurizing; and pressing the coagulation slurry thus filtered against an outer peripheral surface of a drum by a pressing portion, thereby dehydrating the coagulation slurry by pressure exerted thereon, wherein the carbon black has an acidic functional group on a surface thereof, and the amount of an acidic functional group of the carbon black is in the range of 0.2 μeq/m 2 to 3.0 μeq/m 2, wherein the amount of an acidic functional group (μeq/m 2) of the carbon black is determined by neutralization titration by a base, including: adding 2 g to 5 g of the carbon black to 50 mL of 0.976 N sodium hydrogen carbonate and agitating the mixture for 6 hours; filtering the carbon black out from a resulting reaction solution; adding 0.05 N an aqueous solution of hydrochloric acid to the reaction solution and then carrying out neutralization titration of the reaction solution by 0.05 N an aqueous solution of sodium hydroxide until pH of the reaction solution reaches 7.0, to determine an amount of carboxyl group; dividing the amount of carboxyl group thus determined, by the nitrogen adsorption specific surface area (N 2 SA; m 2 /g), to obtain an amount of carboxyl group (μeq/m 2) formed per unit surface area of the carbon black; and regarding the amount of carboxyl group (μeq/m 2) formed per unit surface area as the amount of an acidic functional group (μeq/m 2). filtering the coagulation slurry through a filter by gravity and depressurizing; and pressing the coagulation slurry thus filtered against an outer peripheral surface of a drum by a pressing portion, thereby dehydrating the coagulation slurry by pressure exerted thereon, wherein the carbon black has an acidic functional group on a surface thereof, and the amount of an acidic functional group of the carbon black is in the range of 0.2 μeq/m 2 to 3.0 μeq/m 2, wherein the amount of an acidic functional group (μeq/m 2) of the carbon black is determined by neutralization titration by a base, including: adding 2 g to 5 g of the carbon black to 50 mL of 0.976 N sodium hydrogen carbonate and agitating the mixture for 6 hours; filtering the carbon black out from a resulting reaction solution; adding 0.05 N an aqueous solution of hydrochloric acid to the reaction solution and then carrying out neutralization titration of the reaction solution by 0.05 N an aqueous solution of sodium hydroxide until pH of the reaction solution reaches 7.0, to determine an amount of carboxyl group; dividing the amount of carboxyl group thus determined, by the nitrogen adsorption specific surface area (N 2 SA; m 2 /g), to obtain an amount of carboxyl group (μeq/m 2) formed per unit surface area of the carbon black; and regarding the amount of carboxyl group (μeq/m 2) formed per unit surface area as the amount of an acidic functional group (μeq/m 2). adding 2 g to 5 g of the carbon black to 50 mL of 0.976 N sodium hydrogen carbonate and agitating the mixture for 6 hours; filtering the carbon black out from a resulting reaction solution; adding 0.05 N an aqueous solution of hydrochloric acid to the reaction solution and then carrying out neutralization titration of the reaction solution by 0.05 N an aqueous solution of sodium hydroxide until pH of the reaction solution reaches 7.0, to determine an amount of carboxyl group; dividing the amount of carboxyl group thus determined, by the nitrogen adsorption specific surface area (N 2 SA; m 2 /g), to obtain an amount of carboxyl group (μeq/m 2) formed per unit surface area of the carbon black; and regarding the amount of carboxyl group (μeq/m 2) formed per unit surface area as the amount of an acidic functional group (μeq/m 2).